.H0 "Discussion
.P
This main chapter discusses the practical work done in the mmh project.
It is structured along the goals to achieve.
The concrete work done
is described in the examples of how the general goals were achieved.
The discussion compares the current version of mmh with the state of
nmh just before the mmh project started, i.e. Fall 2011.
Current changes of nmh will be mentioned only as side notes.
.\" XXX where do I discuss the parallel development of nmh?



.H1 "Streamlining

.P
MH had been considered an all-in-one system for mail handling.
The community around nmh has a similar understanding.
In fundamental difference, mmh shall be a MUA only.
I believe that the development of all-in-one mail systems is obsolete.
Today, email is too complex to be fully covered by single projects.
Such a project won't be able to excel in all aspects.
Instead, the aspects of email should be covered my multiple projects,
which then can be combined to form a complete system.
Excellent implementations for the various aspects of email exist already.
Just to name three examples: Postfix is a specialized MTA,
Procmail is a specialized MDA, and Fetchmail is a specialized MRA.
I believe that it is best to use such specialized tools instead of
providing the same function again as a side-component in the project.
.P
Doing something well, requires to focus on a small set of specific aspects.
Under the assumption that focused development produces better results
in the particular area, specialized projects will be superior
in their field of focus.
Hence, all-in-one mail system projects \(en no matter if monolithic
or modular \(en will never be the best choice in any of the fields.
Even in providing the best consistent all-in-one system they are likely
to be beaten by projects that focus only on integrating existing mail
components to a homogeneous system.
.P
The limiting resource in Free Software community development
is usually man power.
If the development power is spread over a large development area,
it becomes even more difficult to compete with the specialists in the
various fields.
The concrete situation for MH-based mail systems is even tougher,
given the small and aged community, including both developers and users,
it has.
.P
In consequence, I believe that the available development resources
should focus on the point where MH is most unique.
This is clearly the user interface \(en the MUA.
Peripheral parts should be removed to streamline mmh for the MUA task.


.H2 "Mail Transfer Facilities
.P
In contrast to nmh, which also provides mail submission and mail retrieval
agents, mmh is a MUA only.
This general difference initiated the development of mmh.
Removing the mail transfer facilities had been the first work task
in the mmh project.
.P
Focusing on one mail agent role only is motivated by Eric Allman's
experience with Sendmail.
He identified limiting Sendmail the MTA task had be one reason for
its success:
.[ [
costales sendmail
.], p. xviii]
.QS
Second, I limited myself to the routing function \(en
I wouldn't write user agents or delivery back-ends.
This was a departure of the dominant through of the time,
in which routing logic, local delivery, and often the network code
were incorporated directly into the user agents.
.QE
.P
In mmh, the Mail Submission Agent (MSA) is called
\fIMessage Transfer Service\fP (MTS).
This facility, implemented by the
.Pn post
command, established network connections and spoke SMTP to submit
messages for relay to the outside world.
The changes in email demanded changes in this part of nmh too.
Encryption and authentication for network connections
needed to be supported, hence TLS and SASL were introduced into nmh.
This added complexity to nmh without improving it in its core functions.
Also, keeping up with recent developments in the field of
mail transfer requires development power and specialists.
In mmh this whole facility was simply cut off.
.Ci f6aa95b724fd8c791164abe7ee5468bf5c34f226
.Ci fecd5d34f65597a4dfa16aeabea7d74b191532c3
.Ci 156d35f6425bea4c1ed3c4c79783dc613379c65b
Instead, mmh depends on an external MSA.
The only outgoing interface available to mmh is the
.Pn sendmail
command, which almost any MSA provides.
If not, a wrapper program can be written.
It must read the message from the standard input, extract the
recipient addresses from the message header, and hand the message
over to the MSA.
For example, a wrapper script for qmail would be:
.VS
#!/bin/sh
# ignore command line arguments
exec qmail-inject
VE
The requirement to parse the recipient addresses out of the message header 
is likely to be removed in the future.
Then mmh would give the recipient addresses as command line arguments.
This appears to be the better interface.
.\" XXX implement it
.P
To retrieve mail, the
.Pn inc
command acted as Mail Retrieval Agent (MRA).
It established network connections
and spoke POP3 to retrieve mail from remote servers.
As with mail submission, the network connections required encryption and
authentication, thus TLS and SASL were added.
Support for message retrieval through IMAP will become necessary
to be added soon, too, and likewise for any other changes in mail transfer.
Not so for mmh because it has dropped the support for retrieving mail
from remote locations.
.Ci ab7b48411962d26439f92f35ed084d3d6275459c
Instead, it depends on an external tool to cover this task.
In mmh exist two paths for messages to enter mmh's mail storage:
(1) Mail can be incorporated with
.Pn inc
from the system maildrop, or (2) with
.Pn rcvstore
by reading them, one at a time, from the standard input.
.P
With the removal of the MSA and MRA, mmh converted from an all-in-one
mail system to being a MUA only.
Now, of course, mmh depends on third-party software.
An external MSA is required to transfer mail to the outside world;
an external MRA is required to retrieve mail from remote machines.
There exist excellent implementations of such software,
which do this specific task likely better than the internal
versions had done it.
Also, the best suiting programs can be freely chosen.
.P
As it had already been possible to use an external MSA or MRA,
why not keep the internal version for convenience?
The question whether there is sense in having a fall-back pager in all
the command line tools, for the cases when
.Pn more
or
.Pn less
aren't available, appears to be ridiculous.
Of course, MSAs and MRAs are more complex than text pagers
and not necessarily available but still the concept of orthogonal
design holds: ``Write programs that do one thing and do it well.''
.[
mcilroy unix phil
p. 53
.]
.[
mcilroy bstj foreword
.]
Here, this part of the Unix philosophy was applied not only
to the programs but to the project itself.
In other words:
``Develop projects that focus on one thing and do it well.''
Projects grown complex should be split for the same reasons programs grown
complex should be split.
If it is conceptionally more elegant to have the MSA and MRA as
separate projects then they should be separated.
This is the case here, in my opinion.
The RFCs propose this separation by clearly distinguishing the different
mail handling tasks.
.[
rfc 821
.]
The small interfaces between the mail agents support the separation.
.P
In the beginning, email had been small and simple.
At that time,
.Pn /bin/mail
had covered anything there was to email and still had been small
and simple.
Later, the essential complexity of email increased.
(Essential complexity is the complexity defined by the problem itself.\0
.[[
brooks no silver bullet
.]])
Email systems reacted to this change: They grew.
RFCs started to introduce the concept of mail agents to separate the
various tasks because they became more extensive and new tasks appeared.
As the mail systems grew even more, parts were split off.
In nmh, for instance, the POP server, which was included in the original
MH, was removed.
Now is the time to go one step further and split the MSA and MRA off, too.
Not only does this decrease the code size of the project,
but, more important, it unburdens mmh of the whole field of
message transfer with all its implications for the project.
There is no more need to concern with changes in network transfer.
This independence is received by depending on an external program
that covers the field.
Today, this is a reasonable exchange.
.P
Functionality can be added in three different ways:
.BU
Implementing the function originally in the project.
.BU
Depending on a library that provides the function.
.BU
Depending on a program that provides the function.
.P
Whereas adding the function originally to the project increases the
code size most and requires most maintenance and development work,
it makes the project most independent of other software.
Using libraries or external programs require less maintenance work
but introduces dependencies on external software.
Programs have the smallest interfaces and provide the best separation
but possibly limit the information exchange.
External libraries are stronger connected than external programs,
thus information can be exchanged more flexible.
Adding code to a project increases maintenance work.
.\" XXX ref
Implementing complex functions originally in the project adds
a lot of code.
This should be avoided if possible.
Hence, the dependencies only change in kind, not in their existence.
In mmh, library dependencies on
.Pn libsasl2
and
.Pn libcrypto /\c
.Pn libssl
were treated against program dependencies on an MSA and an MRA.
This also meant treating build-time dependencies against run-time
dependencies.
Besides program dependencies providing the stronger separation
and being more flexible, they also allowed
over 6\|000 lines of code to be removed from mmh.
This made mmh's code base about 12\|% smaller.
Reducing the project's code size by such an amount without actually
losing functionality is a convincing argument.
Actually, as external MSAs and MRAs are likely superior to the
project's internal versions, the common user even gains functionality.
.P
Users of MH should not have problems to set up an external MSA and MRA.
Also, the popular MSAs and MRAs have large communities and a lot
of documentation available.
Choices for MSAs range from full-featured MTAs like
.I Postfix
over mid-size MTAs like
.I masqmail
and
.I dma
to small forwarders like
.I ssmtp
and
.I nullmailer .
Choices for MRAs include
.I fetchmail ,
.I getmail ,
.I mpop
and
.I fdm .


.H2 "Non-MUA Tools
.P
One goal of mmh is to remove the tools that are not part of the MUA's task.
Further more, any tools that don't improve the MUA's job significantly
should be removed.
Loosely related and rarely used tools distract from the lean appearance.
They require maintenance work without adding much to the core task.
By removing these tools, the project shall become more streamlined
and focused.
In mmh the following tools are not available anymore:
.BU
.Pn conflict
was removed
.Ci 8b235097cbd11d728c07b966cf131aa7133ce5a9
because it is a mail system maintenance tool that is not MUA-related.
It even checked
.Fn /etc/passwd
and
.Fn /etc/group
for consistency, which is completely unrelated to email.
A tool like
.Pn conflict
is surely useful, but it should not be shipped with mmh.
.\" XXX historic reasons?
.BU
.Pn rcvtty
was removed
.Ci 14767c94b3827be7c867196467ed7aea5f6f49b0
because its use case of writing to the user's terminal
on receiving of mail is obsolete.
If users like to be informed of new mail, the shell's
.Ev MAILPATH
variable or graphical notifications are technically more appealing.
Writing directly to terminals is hardly ever wanted today.
If though one wants to have it this way, the standard tool
.Pn write
can be used in a way similar to:
.VS
scan -file - | write `id -un`
VE
.BU
.Pn viamail
was removed
.Ci eda72d6a7a7c20ff123043fb7f19c509ea01f932
when the new attachment system was activated, because
.Pn forw
could then cover the task itself.
The program
.Pn sendfiles
was rewritten as a shell script wrapper around
.Pn forw .
.Ci 0e82199cf3c991a173e0ac8aa776efdb3ded61e6
.BU
.Pn msgchk
was removed
.Ci bb9360ead7eb7a3fedcce2eeedfc660014e41dbe ,
because it lost its use case when POP support was removed.
A call to
.Pn msgchk
provided hardly more information than:
.VS
ls -l /var/mail/meillo
VE
It did distinguish between old and new mail, but
this detail information can be retrieved with
.Pn stat (1),
too.
A small shell script could be written to print the information
in a similar way, if truly necessary.
As mmh's
.Pn inc
only incorporates mail from the user's local maildrop,
and thus no data transfers over slow networks are involved,
there's hardly any need to check for new mail before incorporating it.
.BU
.Pn msh
was removed
.Ci 916690191222433a6923a4be54b0d8f6ac01bd02
because the tool was in conflict with the philosophy of MH.
It provided an interactive shell to access the features of MH,
but it wasn't just a shell, tailored to the needs of mail handling.
Instead it was one large program that had several MH tools built in.
This conflicts with the major feature of MH of being a tool chest.
.Pn msh 's
main use case had been accessing Bulletin Boards, which have seized to
be popular.
.P
Removing
.Pn msh ,
together with the truly archaic code relicts
.Pn vmh
and
.Pn wmh ,
saved more than 7\|000 lines of C code \(en
about 15\|% of the project's original source code amount.
Having less code \(en with equal readability, of course \(en
for the same functionality is an advantage.
Less code means less bugs and less maintenance work.
As
.Pn rcvtty
and
.Pn msgchk
are assumed to be rarely used and can be implemented in different ways,
why should one keep them?
Removing them streamlines mmh.
.Pn viamail 's
use case is now partly obsolete and partly covered by
.Pn forw ,
hence there's no reason to still maintain it.
.Pn conflict
is not related to the mail client, and
.Pn msh
conflicts with the basic concept of MH.
Theses two tools might still be useful, but they should not be part of mmh.
.P
Finally, there's
.Pn slocal .
.Pn slocal
is an MDA and thus not directly MUA-related.
It should be removed from mmh, because including it conflicts with
the idea that mmh is a MUA only.
.Pn slocal
should rather become a separate project.
However,
.Pn slocal
provides rule-based processing of messages, like filing them into
different folders, which is otherwise not available in mmh.
Although
.Pn slocal
does neither pull in dependencies nor does it include a separate
technical area (cf. Sec. XXX), still,
it accounts for about 1\|000 lines of code that need to be maintained.
As
.Pn slocal
is almost self-standing, it should be split off into a separate project.
This would cut the strong connection between the MUA mmh and the MDA
.Pn slocal .
For anyone not using MH,
.Pn slocal
would become yet another independent MDA, like
.I procmail .
Then
.Pn slocal
could be installed without the complete MH system.
Likewise, mmh users could decide to use
.I procmail
without having a second, unused MDA,
.Pn slocal ,
installed.
That appears to be conceptionally the best solution.
Yet,
.Pn slocal
is not split off.
I defer the decision over
.Pn slocal
in need for deeper investigation.
In the meanwhile, it remains part of mmh.
That does not hurt because
.Pn slocal
is unrelated to the rest of the project.


.H2 "\fLshow\fP and \fPmhshow\fP
.P
Since the very beginning \(en already in the first concept paper \(en
.Pn show
had been MH's message display program.
.Pn show
mapped message numbers and sequences to files and invoked
.Pn mhl
to have the files formatted.
With MIME, this approach wasn't sufficient anymore.
MIME messages can consist of multiple parts. Some parts are not
directly displayable and text content might be encoded in
foreign charsets.
.Pn show 's
understanding of messages and
.Pn mhl 's
display capabilities couldn't cope with the task any longer.
.P
Instead of extending these tools, additional tools were written from
scratch and added to the MH tool chest.
Doing so is encouraged by the tool chest approach.
Modular design is a great advantage for extending a system,
as new tools can be added without interfering with existing ones.
First, the new MIME features were added in form of the single program
.Pn mhn .
The command
.Cl "mhn -show 42
would show the MIME message numbered 42.
With the 1.0 release of nmh in February 1999, Richard Coleman finished
the split of
.Pn mhn
into a set of specialized tools, which together covered the
multiple aspects of MIME.
One of them was
.Pn mhshow ,
which replaced
.Cl "mhn -show" .
It was capable of displaying MIME messages appropriately.
.P
From then on, two message display tools were part of nmh,
.Pn show
and
.Pn mhshow .
To ease the life of users,
.Pn show
was extended to automatically hand the job over to
.Pn mhshow
if displaying the message would be beyond
.Pn show 's
abilities.
In consequence, the user would simply invoke
.Pn show
(possibly through
.Pn next
or
.Pn prev )
and get the message printed with either
.Pn show
or
.Pn mhshow ,
whatever was more appropriate.
.P
Having two similar tools for essentially the same task is redundant.
Usually,
users wouldn't distinguish between
.Pn show
and
.Pn mhshow
in their daily mail reading.
Having two separate display programs was therefore mainly unnecessary
from a user's point of view.
Besides, the development of both programs needed to be in sync,
to ensure that the programs behaved in a similar way,
because they were used like a single tool.
Different behavior would have surprised the user.
.P
Today, non-MIME messages are rather seen to be a special case of
MIME messages, although it is the other way round.
As
.Pn mhshow
had already be able to display non-MIME messages, it appeared natural
to drop
.Pn show
in favor of using
.Pn mhshow
exclusively.
.Ci 4c1efddfd499300c7e74263e57d8aa137e84c853
Removing
.Pn show
is no loss in function, because functionally
.Pn mhshow
covers it completely.
The old behavior of
.Pn show
can still be emulated with the simple command line:
.VS
mhl `mhpath c`
VE
.P
For convenience,
.Pn mhshow
was renamed to
.Pn show
after
.Pn show
was gone.
It is clear that such a rename may confuse future developers when
trying to understand the history.
Nevertheless, I consider the convenience on the user's side,
to call
.Pn show
when they want a message to be displayed, to outweigh the inconvenience
on the developer's side when understanding the project history.
.P
To prepare for the transition,
.Pn mhshow
was reworked to behave more like
.Pn show
first.
(cf. Sec. XXX)
Once the tools behaved more alike, the replacing appeared to be
even more natural.
Today, mmh's new
.Pn show
became the one single message display program again, with the difference
that today it handles MIME messages as well as non-MIME messages.
The outcome of the transition is one program less to maintain,
no second display program for users to deal with,
and less system complexity.
.P
Still, removing the old
.Pn show
hurts in one regard: It had been such a simple program.
Its lean elegance is missing to the new
.Pn show .
But there is no chance;
supporting MIME demands for higher essential complexity.


.H2 "Configure Options
.P
Customization is a double-edged sword.
It allows better suiting setups, but not for free.
There is the cost of code complexity to be able to customize.
There is the cost of less tested setups, because there are
more possible setups and especially corner-cases.
And, there is the cost of choice itself.
The code complexity directly affects the developers.
Less tested code affects both, users and developers.
The problem of choice affects the users, for once by having to
choose, but also by more complex interfaces that require more documentation.
Whenever options add little advantages, they should be considered for
removal.
I have reduced the number of project-specific configure options from 
fifteen to three.

.U3 "Mail Transfer Facilities
.P
With the removal of the mail transfer facilities five configure
options vanished:
.P
The switches
.Sw --with-tls
and
.Sw --with-cyrus-sasl
had activated the support for transfer encryption and authentication.
This is not needed anymore.
.Ci fecd5d34f65597a4dfa16aeabea7d74b191532c3
.Ci 156d35f6425bea4c1ed3c4c79783dc613379c65b
.P
The configure switch
.Sw --enable-pop
activated the message retrieval facility.
The code area that would be conditionally compiled in for TLS and SASL
support had been small.
The conditionally compiled code area for POP support had been much larger.
Whereas the code base changes would only slightly change on toggling
TLS or SASL support, it changed much on toggling POP support.
The changes in the code base could hardly be overviewed.
By having POP support togglable a second code base had been created,
one that needed to be tested.
This situation is basically similar for the conditional TLS and SASL  
code, but there the changes are minor and can yet be overviewed.
Still, conditional compilation of a code base creates variations
of the original program.
More variations require more testing and maintenance work.
.P
Two other options only specified default configuration values:
.Sw --with-mts
defined the default transport service, either
.Ar smtp
or
.Ar sendmail .
In mmh this fixed to
.Ar sendmail .
.Ci f6aa95b724fd8c791164abe7ee5468bf5c34f226
With
.Sw --with-smtpservers
default SMTP servers for the
.Ar smtp
transport service could be specified.
.Ci 128545e06224233b7e91fc4c83f8830252fe16c9
Both of them became irrelevant.

.U3 "Backup Prefix
.P
The backup prefix is the string that was prepended to message
filenames to tag them as deleted.
By default it had been the comma character `\f(CW,\fP'.
In July 2000, Kimmo Suominen introduced
the configure option
.Sw --with-hash-backup
to change the default to the hash symbol `\f(CW#\fP'.
The choice was probably personal preference, because first, the
option was named
.Sw --with-backup-prefix.
and had the prefix symbol as argument.
But giving the hash symbol as argument caused too many problems
for Autoconf,
thus the option was limited to use the hash symbol as the default prefix.
This supports the assumption, that the choice for the hash was
personal preference only.
Being related or not, words that start with the hash symbol
introduce a comment in the Unix shell.
Thus, the command line
.Cl "rm #13 #15
calls
.Pn rm
without arguments because the first hash symbol starts the comment
that reaches until the end of the line.
To delete the backup files,
.Cl "rm ./#13 ./#15"
needs to be used.
Using the hash as backup prefix can be seen as a precaution against
data loss.
.P
I removed the configure option but added the profile entry
.Pe backup-prefix ,
which allows to specify an arbitrary string as backup prefix.
.Ci 6c40d481d661d532dd527eaf34cebb6d3f8ed086
Profile entries are the common method to change mmh's behavior.
This change did not remove the choice but moved it to a location where
it suited better.
.P
Eventually, however, the new trash folder concept
.Cf "Sec. XXX
obsoleted the concept of the backup prefix completely.
.Ci 8edc5aaf86f9f77124664f6801bc6c6cdf258173
.\" (Well, there still are corner-cases to remove until the backup
.\" prefix can be laid to rest, eventually.)
.\" FIXME: Do this work in the code!

.U3 "Editor and Pager
.P
The two configure options
.CW --with-editor=EDITOR
.CW --with-pager=PAGER
were used to specify the default editor and pager at configure time.
Doing so at configure time made sense in the eighties,
when the set of available editors and pagers varied much across
different systems.
Today, the situation is more homogeneous.
The programs
.Pn vi
and
.Pn more
can be expected to be available on every Unix system,
as they are specified by POSIX since two decades.
(The specifications for
.Pn vi
and
.Pn more
appeared in
.[
posix 1987
.]
and,
.[
posix 1992
.]
respectively.)
As a first step, these two tools were hard-coded as defaults.
.Ci 5d43a99db70c12a673028c7758c20cbe3e13ef5f
Not changed were the
.Pe editor
and
.Pe moreproc
profile entries, which allowed the user to override the system defaults.
Later, the concept was reworked to respect the standard environment
variables
.Ev VISUAL
and
.Ev PAGER
if they are set.
Today, mmh determines the editor to use in the following order,
taking the first available and non-empty item:
.IP (1)
Environment variable
.Ev MMHEDITOR
.IP (2)
Profile entry
.Pe Editor
.IP (3)
Environment variable
.Ev VISUAL
.IP (4)
Environment variable
.Ev EDITOR
.IP (5)
Command
.Pn vi .
.P
.Ci f85f4b7ae62e3d05a945dcd46ead51f0a2a89a9b
.P
The pager to use is determined in a similar order,
also taking the first available and non-empty item:
.IP (1)
Environment variable
.Ev MMHPAGER
.IP (2)
Profile entry
.Pe Pager
(replaces
.Pe moreproc )
.IP (3)
Environment variable
.Ev PAGER
.IP (4)
Command
.Pn more .
.P
.Ci 0c4214ea2aec6497d0d67b436bbee9bc1d225f1e
.P
By respecting the
.Ev VISUAL /\c
.Ev EDITOR
and
.Ev PAGER
environment variables,
the new behavior confirms better to the common style on Unix systems.
Additionally, the new approach is more uniform and clearer to users.


.U3 "ndbm
.P
.Pn slocal
used to depend on
.I ndbm ,
a database library.
The database is used to store the `\fLMessage-ID\fP's of all
messages delivered.
This enables
.Pn slocal
to suppress delivering the same message to the same user twice.
(This features was enabled by the
.Sw -suppressdup
switch.)
.P
A variety of versions of the database library exist.
.[
wolter unix incompat notes dbm
.]
Complicated autoconf code was needed to detect them correctly.
Further more, the configure switches
.Sw --with-ndbm=ARG
and
.Sw --with-ndbmheader=ARG
were added to help with difficult setups that would
not be detected automatically or correctly.
.P
By removing the suppress duplicates feature of
.Pn slocal ,
the dependency on
.I ndbm
vanished and 120 lines of complex autoconf code could be saved.
.Ci ecd6d6a20cb7a1507e3a20d6c4cb3a1cf14c6bbf
The change removed functionality too, but that is minor to the
improvement by dropping the dependency and the complex autoconf code.

.U3 "mh-e Support
.P
The configure option
.Sw --disable-mhe
was removed when the mh-e support was reworked. 
Mh-e is the Emacs front-end to MH.
It requires MH to provide minor additional functions.
The
.Sw --disable-mhe
configure option could switch these extensions off.
After removing the support for old versions of mh-e,
only the
.Sw -build
switches of
.Pn forw
and
.Pn repl
are left to be mh-e extensions.
They are now always built in because they add little code and complexity.
In consequence, the
.Sw --disable-mhe
configure option was removed
.Ci a7ce7b4a580d77b6c2c4d980812beb589aa4c643
Removing the option removed a second code setup that would have
needed to be tested.
This change was first done in nmh and thereafter merged into mmh.
.P
The interface changes in mmh require mh-e to be adjusted in order
to be able to use mmh as back-end.
This will require minor changes to mh-e, but removing the
.Sw -build
switches would require more rework.

.U3 "Masquerading
.P
The configure option
.Sw --enable-masquerade
could take up to three arguments:
`draft_from', `mmailid', and `username_extension'.
They activated different types of address masquerading.
All of them were implemented in the SMTP-speaking
.Pn post
command, which provided an MSA.
Address masquerading is an MTA's task and mmh does not cover
this field anymore.
Hence, true masquerading needs to be implemented in the external MTA.
.P
The
.I mmailid
masquerading type is the oldest one of the three and the only one
available in the original MH.
It provided a
.I username
to
.I fakeusername
mapping, based on the password file's GECOS field.
The man page
.Mp mh-tailor(5)
described the use case as being the following:
.QS
This is useful if you want the messages you send to always
appear to come from the name of an MTA alias rather than your
actual account name.  For instance, many organizations set up
`First.Last' sendmail aliases for all users.  If this is
the case, the GECOS field for each user should look like:
``First [Middle] Last <First.Last>''
.QE
.P
As mmh sends outgoing mail via the local MTA only,
the best location to do such global rewrites is there.
Besides, the MTA is conceptionally the right location because it
does the reverse mapping for incoming mail (aliasing), too.
Further more, masquerading set up there is readily available for all
mail software on the system.
Hence, mmailid masquerading was removed.
.Ci 0836c8000ccb34b59410ef1c15b1b7feac70ce5f
.P
The
.I username_extension
masquerading type did not replace the username but would append a suffix,
specified by the
.Ev USERNAME_EXTENSION
environment variable, to it.
This provided support for the
.I user-extension
feature of qmail and the similar
.I "plussed user
processing of sendmail.
The decision to remove this username_extension masquerading was
motivated by the fact that
.Pn spost
hadn't supported it already.
.Ci 2abae0bfd0ad5bf898461e50aa4b466d641f23d9
Username extensions are possible in mmh, but less convenient to use.
.\" XXX format file %(getenv USERNAME_EXTENSION)
.P
The
.I draft_from
masquerading type instructed
.Pn post
to use the value of the
.Hd From
header field as SMTP envelope sender.
Sender addresses could be replaced completely.
.Ci b14ea6073f77b4359aaf3fddd0e105989db9
Mmh offers a kind of masquerading similar in effect, but
with technical differences.
As mmh does not transfer messages itself, the local MTA has final control
over the sender's address. Any masquerading mmh introduces may be reverted
by the MTA.
In times of pedantic spam checking, an MTA will take care to use
sensible envelope sender addresses to keep its own reputation up.
Nonetheless, the MUA can set the
.Hd From
header field and thereby propose
a sender address to the MTA.
The MTA may then decide to take that one or generate the canonical sender
address for use as envelope sender address.
.P
In mmh, the MTA will always extract the recipient and sender from the
message header (\c
.Pn sendmail 's
.Sw -t
switch).
The
.Hd From
header field of the draft may be set arbitrary by the user.
If it is missing, the canonical sender address will be generated by the MTA.

.U3 "Remaining Options
.P
Two configure options remain in mmh.
One is the locking method to use:
.Sw --with-locking=[dot|fcntl|flock|lockf] .
The idea of removing all methods except the portable dot locking
and having that one as the default is appealing, but this change
requires deeper technical investigation into the topic.
The other option,
.Sw --enable-debug ,
compiles the programs with debugging symbols and does not strip them.
This option is likely to stay.




.H2 "Command Line Switches
.P
The command line switches of MH tools follow the X Window style.
They are words, introduced by a single dash.
For example:
.Cl "-truncate" .
Every program in mmh has two generic switches:
.Sw -help ,
to print a short message on how to use the program, and 
.Sw -Version ,
to tell what version of mmh the program belongs to.
.P
Switches change the behavior of programs.
Programs that do one thing in one way require no switches.
In most cases, doing something in exactly one way is too limiting.
If there is basically one task to accomplish, but it should be done
in various ways, switches are a good approach to alter the behavior
of a program.
Changing the behavior of programs provides flexibility and customization
to users, but at the same time it complicates the code, documentation and
usage of the program.
.\" XXX: Ref
Therefore, the number of switches should be kept small.
A small set of well-chosen switches does no harm.
But usually, the number of switches increases over time.
Already in 1985, Rose and Romine have identified this as a major
problem of MH:
.[ [
rose romine real work
.], p. 12]
.QS
A complaint often heard about systems which undergo substantial development
by many people over a number of years, is that more and more options are
introduced which add little to the functionality but greatly increase the
amount of information a user needs to know in order to get useful work done.
This is usually referred to as creeping featurism.
.QP
Unfortunately MH, having undergone six years of off-and-on development by
ten or so well-meaning programmers (the present authors included),
suffers mightily from this.
.QE
.P
Being reluctant to adding new switches \(en or `options',
as Rose and Romine call them \(en is one part of a counter-action,
the other part is removing hardly used switches.
Nmh's tools had lots of switches already implemented,
hence, cleaning up by removing some of them was the more important part
of the counter-action.
Removing existing functionality is always difficult because it
breaks programs that use these functions.
Also, for every obsolete feature, there'll always be someone who still
uses it and thus opposes its removal.
This puts the developer into the position,
where sensible improvements to style are regarded as destructive acts.
Yet, living with the featurism is far worse, in my eyes, because
future needs will demand adding further features,
worsening the situation more and more.
Rose and Romine added in a footnote,
``[...]
.Pn send
will no doubt acquire an endless number of switches in the years to come.''
Although clearly humorous, the comment points to the nature of the problem.
Refusing to add any new switches would encounter the problem at its root,
but this is not practical.
New needs will require new switches and it would be unwise to block
them strictly.
Nevertheless, removing obsolete switches still is an effective approach
to deal with the problem.
Working on an experimental branch without an established user base,
eased my work because I did not offend users when I removed existing
functions.
.P
Rose and Romine counted 24 visible and 9 more hidden switches for
.Pn send .
In nmh, they increased up to 32 visible and 12 hidden ones.
At the time of writing, no more than 7 visible switches and 1 hidden switch
have remained in mmh's
.Pn send .
(These numbers include two generic switches, help and version.)
.P
Fig. XXX
.\" XXX Ref
displays the number of switches for each of the tools that is available
in both, nmh and mmh.
The tools are sorted by the number of switches they had in nmh.
Visible and hidden switches were counted,
but not the generic help and version switches.
Whereas in the beginning of the project, the average tool had 11 switches,
now it has no more than 5 \(en only half as many.
If the `no' switches and similar inverse variant are folded onto
their counter-parts, the average tool had 8 switches in pre-mmh times and
has 4 now.
The total number of functional switches in mmh dropped from 465
to 234.

.KS
.in 1c
.so input/switches.grap
.KE

.P
A part of the switches vanished after functions were removed.
This was the case for network mail transfer, for instance.
Sometimes, however, the work flow was the other way:
I looked through the
.Mp mh-chart (7)
man page to identify the tools with apparently too many switches.
Then considering the value of each of the switches by examining
the tool's man page and source code, aided by recherche and testing.
This way, the removal of functions was suggested by the aim to reduce
the number of switches per command.


.U3 "Draft Folder Facility
.P
A change early in the project was the complete transition from
the single draft message to the draft folder facility.
.Ci 337338b404931f06f0db2119c9e145e8ca5a9860
The draft folder facility was introduced in the mid-eighties, when
Rose and Romine called it a ``relatively new feature''.
.[
rose romine real work
.]
Since then, the facility had existed but was inactive by default.
The default activation and the related rework of the tools made it
possible to remove the
.Sw -[no]draftfolder ,
and
.Sw -draftmessage
switches from
.Pn comp ,
.Pn repl ,
.Pn forw ,
.Pn dist ,
.Pn whatnow ,
and
.Pn send .
.Ci 337338b404931f06f0db2119c9e145e8ca5a9860
The only flexibility removed with this change is having multiple
draft folders within one profile.
I consider this a theoretical problem only.
In the same go, the
.Sw -draft
switch of
.Pn anno ,
.Pn refile ,
and
.Pn send
was removed.
The special-casing of `the' draft message became irrelevant after
the rework of the draft system.
(See Sec. XXX.)
Equally,
.Pn comp
lost its
.Sw -file
switch.
The draft folder facility, together with the
.Sw -form
switch, are sufficient.


.U3 "In Place Editing
.P
.Pn anno
had the switches
.Sw -[no]inplace
to either annotate the message in place and thus preserve hard links,
or annotate a copy to replace the original message, breaking hard links.
Following the assumption that linked messages should truly be the
same message, and annotating it should not break the link, the
.Sw -[no]inplace
switches were removed and the previous default
.Sw -inplace
was made the only behavior.
.Ci c8195849d2e366c569271abb0f5f60f4ebf0b4d0
The
.Sw -[no]inplace
switches of
.Pn repl ,
.Pn forw ,
and
.Pn dist
could be removed, too, as they were simply passed through to
.Pn anno .
.P
.Pn burst
also had
.Sw -[no]inplace
switches, but with different meaning.
With
.Sw -inplace ,
the digest had been replaced by the table of contents (i.e. the
introduction text) and the burst messages were placed right
after this message, renumbering all following messages.
Also, any trailing text of the digest was lost, though,
in practice, it usually consists of an end-of-digest marker only.
Nontheless, this behavior appeared less elegant than the
.Sw -noinplace
behavior, which already had been the default.
Nmh's
.Mp burst (1)
man page reads:
.sp \n(PDu
.QS
If -noinplace is given, each digest is preserved, no table
of contents is produced, and the messages contained within
the digest are placed at the end of the folder. Other messages
are not tampered with in any way.
.QE
.LP
The decision to drop the
.Sw -inplace
behavior was supported by the code complexity and the possible data loss
it caused.
.Sw -noinplace
was chosen to be the definitive behavior.
.Ci 68a686adeb39223a5e1ad35e4a24890ec053679d


.U3 "Forms and Format Strings
.P
Historically, the tools that had
.Sw -form
switches to supply a form file had
.Sw -format
switches as well to supply the contents of a form file as a string
on the command line directly.
In consequence, the following two lines equaled:
.VS
scan -form scan.mailx
scan -format "`cat .../scan.mailx`"
VE
The
.Sw -format
switches were dropped in favor for extending the
.Sw -form
switches.
.Ci f51956be123db66b00138f80464d06f030dbb88d
If their argument starts with an equal sign (`='),
then the rest of the argument is taken as a format string,
otherwise the arguments is treated as the name of a format file.
Thus, now the following two lines equal:
.VS
scan -form scan.mailx
scan -form "=`cat .../scan.mailx`"
VE
This rework removed the prefix collision between
.Sw -form
and
.Sw -format .
Now, typing
.Sw -fo
suffices to specify form or format string.
.P
The different meaning of
.Sw -format
for
.Pn repl
and
.Pn forw
was removed in mmh.
.Pn forw
was completely switched to MIME-type forwarding, thus removing the
.Sw -[no]format .
.Ci 6e271608b7b9c23771523f88d23a4d3593010cf1
For
.Pn repl ,
the
.Sw -[no]format
switches were reworked to
.Sw -[no]filter
switches.
.Ci 67411b1f95d6ec987b4c732459e1ba8a8ac192c6
The
.Sw -format
switches of
.Pn send
and
.Pn post ,
which had a third meaning,
were removed likewise.
.Ci f3cb7cde0e6f10451b6848678d95860d512224b9
Eventually, the ambiguity of the
.Sw -format
switches was resolved by not anymore having any such switch in mmh.


.U3 "MIME Tools
.P
The MIME tools, which were once part of
.Pn mhn
[sic!],
had several switches that added little practical value to the programs.
The
.Sw -[no]realsize
switches of
.Pn mhbuild
and
.Pn mhlist
were removed, doing real size calculations always now
.Ci 8d8f1c3abc586c005c904e52c4adbfe694d2201c ,
as
``This provides an accurate count at the expense of a small delay.''
This small delay is not noticable on modern systems.
.P
The
.Sw -[no]check
switches were removed together with the support for
.Hd Content-MD5
header fields.
.[
rfc 1864
.]
.Ci 31dc797eb5178970d68962ca8939da3fd9a8efda
(See Sec. XXX)
.P
The
.Sw -[no]ebcdicsafe
and
.Sw -[no]rfc934mode
switches of
.Pn mhbuild
were removed because they are considered obsolete.
.Ci 01a3480928da485b4d6109d36d751dfa71799d58
.Ci 3363e2624dce0eb8164cf8b3f1ab385c8ff72e88
.P
Content caching of external MIME parts, activated with the
.Sw -rcache
and
.Sw -wcache
switches was completely removed.
.Ci d1fefd9f614e4dc3cda16da6c69133c1b2005269
External MIME parts are rare today, having a caching facility
for them is appears to be unnecessary.
.P
In pre-MIME times,
.Pn mhl
had covered many tasks that are part of MIME handling today.
Therefore,
.Pn mhl
could be simplified to a large extend, reducing the number of its
switches from 21 to 6.
.Ci 350ad6d3542a07639213cf2a4fe524e829c1e7b6
.Ci 0e46503be3c855bddaeae3843e1b659279c35d70


.U3 "Mail Transfer Switches
.P
With the removal of the mail transfer facilities, a lot of switches
vanished automatically.
.Pn inc
lost 9 switches, namely
.Sw -host ,
.Sw -port ,
.Sw -user ,
.Sw -proxy ,
.Sw -snoop ,
.Sw -[no]pack ,
as well as
.Sw -sasl
and
.Sw -saslmech .
.Pn send
and
.Pn post 
lost 11 switches each, namely
.Sw -server ,
.Sw -port ,
.Sw -client ,
.Sw -user ,
.Sw -mail ,
.Sw -saml ,
.Sw -send ,
.Sw -soml ,
.Sw -snoop ,
as well as
.Sw -sasl ,
.Sw -saslmech ,
and
.Sw -tls .
.Pn send
had the switches only to pass them further to
.Pn post ,
because the user would invoke
.Pn post
not directly, but through
.Pn send .
All these switches, except
.Sw -snoop
were usually defined as default switches in the user's profile,
but hardly given in interactive usage.
.P
Of course, those switches did not really ``vanish'', but the configuration
they did was handed over to external MSAs and MRAs.
Instead of setting up the mail transfer in mmh, it is set up in
external tools.
Yet, this simplifies mmh.
Specialized external tools will likely have simple configuration files.
Hence, instead of having one complicated central configuration file,
the configuration of each domain is separate.
Although the user needs to learn to configure each of the tools,
each configuration is likely much simpler.


.U3 "Maildrop Formats
.P
With the removal of MMDF maildrop format support,
.Pn packf
and
.Pn rcvpack
no longer needed their
.Sw -mbox
and
.Sw -mmdf
switches.
.Sw -mbox
is the sole  behavior now.
.Ci 3916ab66ad5d183705ac12357621ea8661afd3c0
In the same go,
.Pn packf
and
.Pn rcvpack
were reworked (see Sec. XXX) and their
.Sw -file
switch became unnecessary.
.Ci ca1023716d4c2ab890696f3e41fa0d94267a940e


.U3 "Terminal Magic
.P
Mmh's tools will no longer clear the screen (\c
.Pn scan 's
and
.Pn mhl 's
.Sw -[no]clear
switches
.Ci e57b17343dcb3ff373ef4dd089fbe778f0c7c270
.Ci 943765e7ac5693ae177fd8d2b5a2440e53ce816e ).
Neither will
.Pn mhl
ring the bell (\c
.Sw -[no]bell
.Ci e11983f44e59d8de236affa5b0d0d3067c192e24 )
nor page the output itself (\c
.Sw -length
.Ci 5b9d883db0318ed2b84bb82dee880d7381f99188 ).
.P
Generally, the pager to use is no longer specified with the
.Sw -[no]moreproc
command line switches for
.Pn mhl
and
.Pn show /\c
.Pn mhshow .
.Ci 39e87a75b5c2d3572ec72e717720b44af291e88a
.P
.Pn prompter
lost its
.Sw -erase
and
.Sw -kill
switches because today the terminal cares for the line editing keys.


.U3 "Header Printing
.P
.Pn folder 's
data output is self-explaining enough that
displaying the header line makes few sense.
Hence, the
.Sw -[no]header
switch was removed and headers are never printed.
.Ci 601cc73d1fa05ce96faa728f036d6c51b91701c7
.P
In
.Pn mhlist ,
the
.Sw -[no]header
switches were removed, too.
.Ci b24f96523aaf60e44e04a3ffb1d22e69a13a602f
But in this case headers are always printed,
because the output is not self-explaining.
.P
.Pn scan
also had
.Sw -[no]header
switches.
Printing the header had been sensible until the introduction of
format strings made it impossible to display the column headings.
Only the folder name and the current date remained to be printed.
As this information can be perfectly retrieved by
.Pn folder
and
.Pn date ,
consequently, the switches were removed.
.Ci c477dc5d1d03fa6d9a8ab3dd3508c63cbddc044e
.P
By removing all
.Sw -header
switches, the collision with
.Sw -help
on the first two letters was resolved.
Currently,
.Sw -h
evaluates to
.Sw -help
for all tools of mmh.


.U3 "Suppressing Edits or the WhatNow Shell
.P
The
.Sw -noedit
switch of
.Pn comp ,
.Pn repl ,
.Pn forw ,
.Pn dist ,
and
.Pn whatnow
was removed, but it can now be replaced by specifying
.Sw -editor
with an empty argument.
.Ci 75fca31a5b9d5c1a99c74ab14c94438d8852fba9
(Specifying
.Cl "-editor true
is nearly the same, only differing by the previous editor being set.)
.P
The more important change is the removal of the
.Sw -nowhatnowproc
switch.
.Ci ee4f43cf2ef0084ec698e4e87159a94c01940622
This switch had introduced an awkward behavior, as explained in nmh's
man page for
.Mp comp (1):
.QS
The \-editor editor switch indicates the editor to use for
the initial edit. Upon exiting from the editor, comp will
invoke the whatnow program. See whatnow(1) for a discussion
of available options. The invocation of this program can be
inhibited by using the \-nowhatnowproc switch. (In truth of
fact, it is the whatnow program which starts the initial
edit. Hence, \-nowhatnowproc will prevent any edit from
occurring.)
.QE
.P
Effectively, the
.Sw -nowhatnowproc
switch creates only a draft message.
As
.Cl "-whatnowproc true
causes the same behavior, the
.Sw -nowhatnowproc
switch was removed for being redundant.
Likely, the
.Sw -nowhatnowproc
switch was intended to be used by front-ends.


.U3 "Compatibility Switches
.BU
The hidden
.Sw -[no]total
switches of
.Pn flist .
They were simply the inverse of the visible
.Sw -[no]fast
switches:
.Sw -total
was
.Sw -nofast
and
.Sw -nototal
was
.Sw -fast .
I removed the
.Sw -[no]total
legacy.
.Ci ea21fe2c4bd23c639bef251398fae809875732ec
.BU
The
.Sw -subject
switch of
.Pn sortm
existed for compatibility only.
It can be fully replaced by
.Cl "-textfield subject
thus it was removed.
.Ci 00140a3c86e9def69d98ba2ffd4d6e50ef6326ea


.U3 "Various
.BU
In order to avoid prefix collisions among switch names, the
.Sw -version
switch was renamed to
.Sw -Version
(with capital `V').
.Ci 32b2354dbaf4bf934936eb5b102a4a3d2fdd209a
Every program has the
.Sw -version
switch but its first three letters collided with the
.Sw -verbose
switch, present in many programs.
The rename solved this problem once for all.
Although this rename breaks a basic interface, having the
.Sw -V
abbreviation to display the version information, isn't all too bad.
.BU
.Sw -[no]preserve
of
.Pn refile
was removed because what use was it anyway?
.QS
Normally when a message is refiled, for each destination
folder it is assigned the number which is one above the current
highest message number in that folder. Use of the
\-preserv [sic!] switch will override this message renaming, and try
to preserve the number of the message. If a conflict for a
particular folder occurs when using the \-preserve switch,
then refile will use the next available message number which
is above the message number you wish to preserve.
.QE
.BU
The removal of the
.Sw -[no]reverse
switches of
.Pn scan
.Ci 8edc5aaf86f9f77124664f6801bc6c6cdf258173
is a bug fix, supported by the comments
``\-[no]reverse under #ifdef BERK (I really HATE this)''
by Rose and
``Lists messages in reverse order with the `\-reverse' switch.
This should be considered a bug.'' by Romine in the documentation.
The question remains why neither Rose and Romine had fixed this
bug in the eighties when they wrote these comments nor has anyone
thereafter.


.ig

forw: [no]dashstuffing(mhl)

mhshow: [no]pause [no]serialonly

mhmail: resent queued
inc: snoop, (pop)

mhl: [no]faceproc folder sleep
	[no]dashstuffing(forw) digest list volume number issue number

prompter: [no]doteof

refile: [no]preserve [no]unlink [no]rmmproc

send: [no]forward [no]mime [no]msgid
	[no]push split [no]unique (sasl) width snoop [no]dashstuffing
	attach attachformat
whatnow: (noedit) attach

slocal: [no]suppressdups

spost: [no]filter [no]backup width [no]push idanno
	[no]check(whom) whom(whom)

whom: ???

..


.ig

.P
In the best case, all switches are unambiguous on the first character,
or on the three-letter prefix for the `no' variants.
Reducing switch prefix collisions, shortens the necessary prefix length
the user must type.
Having less switches helps best.

..


.\" XXX: whatnow prompt commands




.H1 "Modernizing
.P
In the over thirty years of MH's existence, its code base was
extended more and more.
New features entered the project and became alternatives to the
existing behavior.
Relicts from several decades have gathered in the code base,
but seldom obsolete features were dropped.
This section describes the removing of old code
and the modernizing of the default setup.
It focuses on the functional aspect only;
the non-functional aspects of code style are discussed in
.\" FIXME REF
Sec. XXX.


.H2 "Code Relicts
.P
My position to drop obsolete functions of mmh, in order to remove old code,
is much more revolutional than the nmh community likes to have it.
Working on an experimental version, I was able to quickly drop
functionality I considered ancient.
The need for consensus with peers would have slowed this process down.
Without the need to justify my decisions, I was able to rush forward.
In December 2011, Paul Vixie motivated the nmh developers to just
do the work:
.[
paul vixie edginess nmh-workers
.]
.QS
let's stop walking on egg shells with this code base. there's no need to
discuss whether to keep using vfork, just note in [sic!] passing, [...]
we don't need a separate branch for removing vmh
or ridding ourselves of #ifdef's or removing posix replacement functions
or depending on pure ansi/posix "libc".
.QP
these things should each be a day or two of work and the "main branch"
should just be modern. [...]
let's push forward, aggressively.
.QE
.LP
I did so already in the months before.
I pushed forward.
I simply dropped the cruft.
.P
The decision to drop a feature was based on literature research and
careful thinking, but whether having had contact to this particular
feature within my own computer life served as a rule of thumb.
Always, I explained my reasons in the commit messages
in the version control system.
Hence, others can comprehend my view and argue for undoing the change
if I have missed an important aspect.
I was quick in dropping parts.
I rather re-included falsely dropped parts than going a slower pace.
Mmh is experimental work; it required tough decisions.


.U3 "Forking
.P
Being a tool chest, MH creates many processes.
In earlier times
.Fu fork()
had been an expensive system call, because the process's image needed
to be duplicated completely at once.
This was especially painful in the common case when the image gets
replaced by a call to
.Fu exec()
right after having forked the child process.
The
.Fu vfork()
system call was invented to speed up this particular case.
It completely omits the duplication of the image.
On old systems this resulted in significant speed ups.
Therefore MH used
.Fu vfork()
whenever possible.
.P
Modern memory management units support copy-on-write semantics, which make
.Fu fork()
almost as fast as
.Fu vfork() .
The man page of
.Mp vfork (2)
in FreeBSD 8.0 states:
.QS
This system call will be eliminated when proper system sharing mechanisms
are implemented. Users should not depend on the memory sharing semantics
of vfork() as it will, in that case, be made synonymous to fork(2).
.QE
.LP
Vixie supports the removal with the note that ``the last
system on which fork was so slow that an mh user would notice it, was
Eunice. that was 1987''.
.[
nmh-workers vixie edginess
.]
I replaced all calls to
.Fu vfork()
with calls to
.Fu fork() .
.Ci 40821f5c1316e9205a08375e7075909cc9968e7d
.P
Related to the costs of
.Fu fork()
is the probability of its success.
In the eighties, on heavy loaded systems, calls to
.Fu fork()
were prone to failure.
Hence, many of the
.Fu fork()
calls in the code were wrapped into loops to retry the
.Fu fork()
several times, to increase the changes to succeed, eventually.
On modern systems, a failing
.Fu fork()
call is unusual.
Hence, in the rare case when
.Fu fork()
fails, mmh programs simply abort.
.Ci 5fbf37ee68e018998ada61eeab73e035b26834b6


.U3 "Header Fields
.BU
The
.Hd Encrypted
header field was introduced by RFC\|822,
but already marked as legacy in RFC\|2822.
Today, OpenPGP provides the basis for standardized exchange of encrypted
messages [RFC\|4880, RFC\|3156].
Hence, the support for
.Hd Encrypted
header fields is removed in mmh.
.Ci 064527f7b57ab050e5af13e15ad99aeeab125857
.BU
Native support for
.Hd Face
header fields has been removed, as well.
.Ci 8e5be81f784682822f5e868c1bf3c8624682bd23
This feature is similar to the
.Hd X-Face
header field in its intent,
but takes a different approach to store the image.
Instead of encoding the image data directly into the header field,
it contains the hostname and UDP port where the image
date can be retrieved.
There exists even a third Face system,
which is the successor of
.Hd X-Face ,
although it re-uses the
.Hd Face
header field.
It was invented in 2005 and supports colored PNG images.
None of the Face systems described here is popular today.
Hence, mmh has no direct support for them.
.BU
The
.Hd Content-MD5
header field was introduced by RFC\|1864.
It provides detection of data corruption during the transfer.
But it can not ensure verbatim end-to-end delivery of the contents
[RFC\|1864].
The proper approach to verify content integrity in an
end-to-end relationship is the use of digital cryptography.
.\" XXX (RFCs FIXME).
On the other hand, transfer protocols should detect corruption during
the transmission.
The TCP includes a checksum field therefore.
These two approaches in combinations render the
.Hd Content-MD5
header field superfluous.
Not a single one out of 4\|200 messages from two decades
in an nmh-workers mailing list archive contains a
.Hd Content-MD5
header field.
Neither did any of the 60\|000 messages in my personal mail storage.
Removing the support for this header field,
removed the last place where MD5 computation was needed.
.Ci 31dc797eb5178970d68962ca8939da3fd9a8efda
Hence, the MD5 code could be removed as well.
Over 500 lines of code vanished by this one change.


.U3 "MMDF maildrop support
.P
This type of format is conceptionally similar to the mbox format,
but uses a different message delimiter (`\fL^A^A^A^A\fP' instead of
`\fLFrom\0\fP').
Mbox is the de-facto standard maildrop format on Unix,
whereas the MMDF maildrop format became forgotten.
I did drop MMDF maildrop format support.
Mbox is the only packed mailbox format supported in mmh.
.P
The simplifications within the code were moderate.
Mainly, the reading and writing of MMDF mailbox files was removed.
But also, switches of
.Pn packf
and
.Pn rcvpack
could be removed.
.Ci 3916ab66ad5d183705ac12357621ea8661afd3c0
In the message parsing function
.Fn sbr/m_getfld.c ,
knowledge of MMDF packed mail boxes was removed.
.Ci 684ec30d81e1223a282764452f4902ed4ad1c754
Further code structure simplifications may be possible there,
because only one single packed mailbox format is left to be supported.
I have not worked on them yet because
.Fu m_getfld()
is heavily optimized and thus dangerous to touch.
The risk of damaging the intricate workings of the optimized code is
too high.
.\" XXX: move somewhere else
This problem is know to the developers of nmh, too.
They also avoid touching this minefield.


.U3 "Prompter's Control Keys
.P
The program
.Pn prompter
queries the user to fill in a message form.
When used by
.Pn comp
as
.Cl "comp -editor prompter" ,
the resulting behavior is similar to
.Pn mailx .
Apparently,
.Pn prompter
hadn't been touched lately.
Otherwise it's hardly explainable why it
still offered the switches
.Sw -erase
.Ar chr
and
.Sw -kill
.Ar chr
to name the characters for command line editing.
The times when this had been necessary are long time gone.
Today these things work out-of-the-box, and if not, are configured
with the standard tool
.Pn stty .
The switches are removed now
.Ci 0bd9750710cdbab80cfb4036dd87af20afe1552f .


.U3 "Hardcopy Terminal Support
.P
More of a funny anecdote is a check for being connected to a
hardcopy terminal.
It remained in the code until Spring 2012, when I finally removed it
.Ci b7764c4a6b71d37918a97594d866258f154017ca .
I would be truly happy to see such a terminal in action today,
maybe even being able to work on it.
But I fear my chances are null.
.P
The check only prevented a pager to be placed between the printing
program (\c
.Pn mhl )
and the terminal.
In nmh, this could have been ensured statically with the
.Sw -nomoreproc
at the command line, too.
In mmh, setting the profile entry
.Pe Pager
or the environment variable
.Ev PAGER
to
.Pn cat
does the job.




.H2 "Attachments
.P
The mind model of email attachments is unrelated to MIME.
Although the MIME RFCs (2045 through 2049) define the technical
requirements for having attachments, they do not mention the word
``attachment''.
Instead of attachments, MIME talks about ``multi-part message bodies''
[RFC\|2045], a more general concept.
Multi-part messages are messages
``in which one or more different
sets of data are combined in a single body''
[RFC\|2046].
MIME keeps its descriptions generic;
it does not imply specific usage models.
One usage model became prevalent: attachments.
The idea is having a main text document with files of arbitrary kind
attached to it.
In MIME terms, this is a multi-part message having a text part first
and parts of arbitrary type following.
.P
MH's MIME support is a direct implementation of the RFCs.
The perception of the topic described in the RFCs is clearly visible
in MH's implementation.
In result, MH had all the MIME features but no idea of attachments.
But users don't need all the MIME features,
they want convenient attachment handling.


.U3 "Composing MIME Messages
.P
In order to improve the situation on the message composing side,
Jon Steinhart had added an attachment system to nmh in 2002.
.Ci 7480dbc14bc90f2d872d434205c0784704213252
In the file
.Fn docs/README-ATTACHMENTS ,
he described his motivation to do so as such:
.QS
Although nmh contains the necessary functionality for MIME message handing,
the interface to this functionality is pretty obtuse.
There's no way that I'm ever going to convince my partner to write
.Pn mhbuild
composition files!
.QE
.LP
With this change, the mind model of attachments entered nmh.
In the same document:
.QS
These changes simplify the task of managing attachments on draft files.
They allow attachments to be added, listed, and deleted.
MIME messages are automatically created when drafts with attachments
are sent.
.QE
.LP
Unfortunately, the attachment system,
like any new facilities in nmh,
was inactive by default.
.P
During my work in Argentina, I tried to improve the attachment system.
But, because of great opposition in the nmh community,
my patch died as a proposal on the mailing list, after long discussions.
.[
nmh-workers attachment proposal
.]
In January 2012, I extended the patch and applied it to mmh.
.Ci 8ff284ff9167eff8f5349481529332d59ed913b1
In mmh, the attachment system is active by default.
Instead of command line switches, the
.Pe Attachment-Header
profile entry is used to specify
the name of the attachment header field.
It is pre-defined to
.Hd Attach .
.P
To add an attachment to a draft, simply add an attachment header:
.VS
To: bob
Subject: The file you wanted
Attach: /path/to/the/file-bob-wanted
--------
Here it is.
VE
The header field can be added to the draft manually in the editor,
or by using the `attach' command at the WhatNow prompt, or
non-interactively with
.Pn anno :
.VS
anno -append -nodate -component Attach -text /path/to/attachment
VE
Drafts with attachment headers are converted to MIME automatically by
.Pn send .
The conversion to MIME is invisible to the user.
The draft stored in the draft folder is always in source form, with
attachment headers.
If the MIMEification fails, for instance because the file to attach
is not accessible, the original draft is not changed.
.P
The attachment system handles the forwarding of messages, too.
If the attachment header value starts with a plus character (`+'),
like in
.Cl "Attach: +bob 30 42" ,
The given messages in the specified folder will be attached.
This allowed to simplify
.Pn forw .
.Ci f41f04cf4ceca7355232cf7413e59afafccc9550
.P
Closely related to attachments is non-ASCII text content,
because it requires MIME too.
In nmh, the user needed to call `mime' at the WhatNow prompt
to have the draft converted to MIME.
This was necessary whenever the draft contained non-ASCII characters.
If the user did not call `mime', a broken message would be sent.
Therefore, the
.Pe automimeproc
profile entry could be specified to have the `mime' command invoked
automatically each time.
Unfortunately, this approach conflicted with with attachment system
because the draft would already be in MIME format at the time
when the attachment system wanted to MIMEify it.
To use nmh's attachment system, `mime' must not be called at the
WhatNow prompt and
.Pe automimeproc
must not be set in the profile.
But then the case of non-ASCII text without attachment headers was
not caught.
All in all, the solution was complex and irritating.
My patch from December 2010 would have simplified the situation.
.P
Mmh's current solution is even more elaborate.
Any necessary MIMEification is done automatically.
There is no `mime' command at the WhatNow prompt anymore.
The draft will be converted automatically to MIME when either an
attachment header or non-ASCII text is present.
Further more, the special meaning of the hash character (`#')
at line beginnings in the draft message is removed.
Users need not at all deal with the whole topic.
.P
Although the new approach does not anymore support arbitrary MIME
compositions directly, the full power of
.Pn mhbuild
can still be accessed.
Given no attachment headers are included, the user can create
.Pn mhbuild
composition drafts like in nmh.
Then, at the WhatNow prompt, he needs to invoke
.Cl "edit mhbuild
to convert it to MIME.
Because the resulting draft does neither contain non-ASCII characters
nor has it attachment headers, the attachment system will not touch it.
.P
The approach taken in mmh is tailored towards todays most common case:
a text part with possibly attachments.
This case is simplified a lot for users.


.U3 "MIME Type Guessing
.P
The use of
.Pn mhbuild
composition drafts had one notable advantage over attachment headers
from the programmer's point of view: The user provides the appropriate
MIME types for files to include.
The attachment system needs to find out the correct MIME type itself.
This is a difficult task, yet it spares the user irritating work.
Determining the correct MIME type of content is partly mechanical,
partly intelligent work.
Forcing the user to find out the correct MIME type,
forces him to do partly mechanical work.
Letting the computer do the work, can lead to bad choices for difficult
content.
For mmh, the latter option was chosen.
.P
Determining the MIME type by the suffix of the file name is a dumb
approach, yet it is simple to implement and provides good results
for the common cases.
Mmh implements this approach in the
.Pn print-mimetype
script.
.Ci 4b5944268ea0da7bb30598a27857304758ea9b44
Using it is the default choice.
.P
A far better, though less portable, approach is the use of
.Pn file .
This standard tool tries to determine the type of files.
Unfortunately, its capabilities and accuracy varies from system to system.
Additionally, its output was only intended for human beings,
but not to be used by programs.
It varies much.
Nevertheless, modern versions of GNU
.Pn file ,
which is prevalent on the popular GNU/Linux systems,
provides MIME type output in machine-readable form.
Although this solution is highly system-dependent,
it solves the difficult problem well.
On systems where GNU
.Pn file ,
version 5.04 or higher, is available it should be used.
One needs to specify the following profile entry to do so:
.Ci 3baec236a39c5c89a9bda8dbd988d643a21decc6
.VS
Mime-Type-Query: file -b --mime
VE
.LP
Other versions of
.Pn file
might possibly be usable with wrapper scripts to reformat the output.
The diversity among
.Pn file
implementations is great; one needs to check the local variant.
.P
If no MIME type can be determined, text content gets sent as
`text/plain' and anything else under the generic fall-back type
`application/octet-stream'.
It is not possible in mmh to override the automatic MIME type guessing
for a specific file.
To do so, the user would need to know in advance for which file
the automatic guessing does fail, or the system would require interaction.
I consider both cases impractical.
The existing solution should be sufficient.
If not, the user may always fall back to
.Pn mhbuild
composition drafts and ignore the attachment system.


.U3 "Storing Attachments
.P
Extracting MIME parts of a message and storing them to disk is done by
.Pn mhstore .
The program has two operation modes,
.Sw -auto
and
.Sw -noauto .
With the former one, each part is stored under the filename given in the
MIME part's meta information, if available.
This naming information is usually available for modern attachments.
If no filename is available, this MIME part is stored as if
.Sw -noauto
would have been specified.
In the
.Sw -noauto
mode, the parts are processed according to rules, defined by
.Pe mhstore-store-*
profile entries.
These rules define generic filename templates for storing
or commands to post-process the contents in arbitrary ways.
If no matching rule is available the part is stored under a generic
filename, built from message number, MIME part number, and MIME type.
.P
The
.Sw -noauto
mode had been the default in nmh because it was considered safe,
in contrast to the
.Sw -auto
mode.
In mmh,
.Sw -auto
is not dangerous anymore.
Two changes were necessary:
.BU
Any directory path is removed from the proposed filename.
Thus, the files are always stored in the expected directory.
.Ci 41b6eadbcecf63c9a66aa5e582011987494abefb
.BU
Tar files are not extracted automatically any more.
Thus, the rest of the file system will not be touched.
.Ci 94c80042eae3383c812d9552089953f9846b1bb6
.LP
Now, the outcome of mmh's
.Cl "mhstore -auto
can be foreseen from the output of
.Cl "mhlist -verbose" .
.P
The
.Sw -noauto
mode is seen to be more powerful but less convenient.
On the other hand,
.Sw -auto
is safe now and
storing attachments under their original name is intuitive.
Hence,
.Sw -auto
serves better as the default option.
.Ci 3410b680416c49a7617491af38bc1929855a331d
.P
Files are stored into the directory given by the
.Pe Nmh-Storage
profile entry, if set, or
into the current working directory, otherwise.
Storing to different directories is only possible with
.Pe mhstore-store-*
profile entries.
.P
Still, in both modes, existing files get overwritten silently.
This can be considered a bug.
Yet, each other behavior has its draw-backs, too.
Refusing to replace files requires adding a
.Sw -force
option.
Users will likely need to invoke
.Pn mhstore
a second time with
.Sw -force
then.
Eventually, only the user can decide in the concrete case.
This requires interaction, which I like to avoid if possible.
Appending a unique suffix to the filename is another bad option.
For now, the behavior remains as it is.
.P
In mmh, only MIME parts of type message are special in
.Pn mhstore 's
.Sw -auto
mode.
Instead of storing message/rfc822 parts as files to disk,
they are stored as messages into the current mail folder.
The same applies to message/partial, only, the parts are reassembled
automatically before.
Parts of type message/external-body are not automatically retrieved
anymore. Instead, Information on how to retrieve them is output.
Not supporting this rare case saved nearly one thousand lines of code.
.Ci 55e1d8c654ee0f7c45b9361ce34617983b454c32
.\" XXX mention somewhere else too: (The profile entry `nmh-access-ftp'
.\"     and sbr/ruserpass.c for reading ~/.netrc are gone now.)
Not special anymore is `application/octet-stream; type=tar'.
Automatically extracting such MIME parts had been the dangerous part
of the
.Sw -auto
mode.
.Ci 94c80042eae3383c812d9552089953f9846b1bb6



.U3 "Showing MIME Messages
.P
The program
.Pn mhshow
had been written to display MIME messages.
It implemented the conceptional view of the MIME RFCs.
Nmh's
.Pn mhshow
handled each MIME part independently, presenting them separately
to the user.
This does not match today's understanding of email attachments,
where displaying a message is seen to be a single, integrated operation.
Today, email messages are expected to consist of a main text part
plus possibly attachments.
They are not any more seen to be arbitrary MIME hierarchies with
information on how to display the individual parts.
I adjusted
.Pn mhshow 's
behavior to the modern view on the topic.
.P
Note that this section completely ignores the original
.Pn show
program, because it was not capable to display MIME messages
and is no longer part of mmh.
Although
.Pn mhshow
was renamed to
.Pn show
in mmh, this section uses the name
.Pn mhshow ,
in order to avoid confusion.
.P
In mmh, the basic idea is that
.Pn mhshow
should display a message in one single pager session.
Therefore,
.Pn mhshow
invokes a pager session for all its output,
whenever it prints to a terminal.
.Ci a4197ea6ffc5c1550e8b52d5a654bcaaaee04a4e
In consequence,
.Pn mhl
does no more invoke a pager.
.Ci 0e46503be3c855bddaeae3843e1b659279c35d70
With
.Pn mhshow
replacing the original
.Pn show ,
output from
.Pn mhl
does not go to the terminal directly, but through
.Pn mhshow .
Hence,
.Pn mhl
does not need to invoke a pager.
The one and only job of
.Pn mhl
is to format messages or parts of them.
The only place in mmh, where a pager is invoked is
.Pn mhshow .
.P
.Pe mhshow-show-*
profile entries can be used to display MIME parts in a specific way.
For instance, PDF and Postscript files could be converted to plain text
to display them in the terminal.
In mmh, the displaying of MIME parts will always be done serially.
The request to display the MIME type `multipart/parallel' in parallel
is ignored.
It is simply treated as `multipart/mixed'.
.Ci d0581ba306a7299113a346f9b4c46ce97bc4cef6
This could already be requested with the, now removed,
.Sw -serialonly
switch of
.Pn mhshow .
As MIME parts are always processed exclusively , i.e. serially,
the `%e' escape in
.Pe mhshow-show-*
profile entries became useless and was thus removed.
.Ci a20d405db09b7ccca74d3e8c57550883da49e1ae
.P
In the intended setup, only text content would be displayed.
Non-text content would be converted to text by appropriate
.Pe mhshow-show-*
profile entries before, if possible and wanted.
All output would be displayed in a single pager session.
Other kinds of attachments are ignored.
With
.Pe mhshow-show-*
profile entries for them, they can be displayed serially along
the message.
For parallel display, the attachments need to be stored to disk first.
.P
To display text content in foreign charsets, they need to be converted
to the native charset.
Therefore,
.Pe mhshow-charset-*
profile entries used to be needed.
In mmh, the conversion is done automatically by piping the text through
the
.Pn iconv
command, if necessary.
.Ci 2433122c20baccb10b70b49c04c6b0497b5b3b60
Custom
.Pe mhshow-show-*
rules for textual content might need a
.Cl "iconv -f %c %f |
prefix to have the text converted to the native charset.
.P
Although the conversion of foreign charsets to the native one
has improved, it is not consistent enough.
Further work needs to be done and
the basic concepts in this field need to be re-thought.
Though, the default setup of mmh displays message in foreign charsets
correctly without the need to configure anything.


.ig

.P
mhshow/mhstore: Removed support for retrieving message/external-body parts.
These tools won't download the contents automatically anymore. Instead,
they print the information needed to get the contents. If someone should
really receive one of those rare message/external-body messages, he can
do the job manually. We save nearly a thousand lines of code. That's worth
it!
(The profile entry `nmh-access-ftp' and sbr/ruserpass.c for reading
~/.netrc are gone now.)
.Ci 55e1d8c654ee0f7c45b9361ce34617983b454c32

..



.H2 "Digital Cryptography
.P
Signing and encryption.
.P
FIXME



.H2 "Modern Defaults
.P
Nmh has a bunch of convenience-improving features inactive by default,
although one can expect every new user wanting to have them active.
The reason they are inactive by default is the wish to stay compatible
with old versions.
But what is the definition for old versions.
Still, the highly useful draft folder facility is not active by default
although it had been introduced over twenty-five years ago
.[
rose romine real work
.]
\(en the community seems not to care.
This is one of several examples that require new users to build up
their profile before they can access the modern features of nmh.
Without an extensively built-up profile, the setup is hardly usable
for modern emailing.
The point is not the customization of the setup,
but the activating of generally useful facilities.
.P
Yet, the real problem lies less in enabling the features, as this is
straight forward as soon as one knows what he wants.
The real problem is that new users need deep insights into the project
before they find out what they are missing and that nmh actually
provides it already, it just was not activated.
To give an example, I needed one year of using nmh
before I became aware of the existence of the attachment system.
One could argue that this fact disqualifies my reading of the
documentation.
If I would have installed nmh from source back then, I could agree.
Yet, I had used a prepackaged version and had expected that it would
just work.
Nevertheless, I had been convinced by the concepts of MH already
and I am a software developer,
still I required a lot of time to discover the cool features.
How can we expect users to be even more advanced than me,
just to allow them use MH in a convenient and modern way?
Unless they are strongly convinced of the concepts, they will fail.
I have seen friends of me giving up disappointed
before they truly used the system,
although they had been motivated in the beginning.
They suffer hard enough to get used to the toolchest approach,
we should spare them further inconveniences.
.P
Maintaining compatibility for its own sake is for no good.
If any MH implementation would be the back-end of widespread
email clients with large user bases, compatibility would be more
important.
Yet, it appears as if this is not the case.
Hence, compatibility is hardly important for technical reasons.
Its importance originates rather from personal reasons.
Nmh's user base is small and old.
Changing the interfaces would cause inconvenience to long-term users of MH.
It would force them to change their many years old MH configurations.
I do understand this aspect, but it keeps new users from using MH.
By sticking to the old users, new users are kept away.
Yet, the future lies in new users.
Hence, mmh invites new users by providing a convenient and modern setup,
readily usable out-of-the-box.
.P
In mmh, all modern features are active by default.
In consequence, a setup with a profile that defines only the path to the
mail storage, is already convenient to use.
Again, Paul Vixie's ``edginess'' appeal supports the direction I took:
``the `main branch' should just be modern''.
.[
paul vixie edginess nmh-workers
.]
.P
Modern features that are active in mmh by default include: 
.BU
The attachment system (\c
.Hd Attach ).
.Ci 8ff284ff9167eff8f5349481529332d59ed913b1
.BU
The draft folder facility (\c
.Fn +drafts ).
.Ci 337338b404931f06f0db2119c9e145e8ca5a9860
.BU
The unseen sequence (`u')
.Ci c2360569e1d8d3678e294eb7c1354cb8bf7501c1
and the sequence negation prefix (`!').
.Ci db74c2bd004b2dc9bf8086a6d8bf773ac051f3cc
.BU
Quoting the original message in the reply.
.Ci 67411b1f95d6ec987b4c732459e1ba8a8ac192c6
.BU
Forwarding messages using MIME.
.Ci 6e271608b7b9c23771523f88d23a4d3593010cf1




.H1 "Code Style
.P
Kernighan and Pike have emphasized the importance of style in the
preface of their book:
.[ [
kernighan pike practice of programming
.], p. x]
.QS
Chapter 1 discusses programming style.
Good style is so important to good programming that we have chose
to cover it first.
.QE
This section covers changes in mmh that were motivated by the desire
to improve on style.
Many of them follow the rules given in the quoted book.
.[
kernighan pike practice of programming
.]


.H2 "Style
.P
.U3 "Indentation Style
.P
Indentation styles are the holy cow of programmers.
Again Kernighan and Pike:
.[ [
kernighan pike practice of programming
.], p. 10]
.QS
Programmers have always argued about the layout of programs,
but the specific style is much less important than its consistent
application.
Pick one style, preferably ours, use it consistently, and don't waste
time arguing.
.QE
.P
I agree that the constant application is most important,
but I believe that some styles have advantages over others.
For instance the indentation with tab characters only.
Tab characters directly map to the nesting level \(en
one tab, one level.
Tab characters are flexible because developers can adjust them to
whatever width they like to have.
There is no more need to run
.Pn unexpand
or
.Pn entab
programs to ensure the correct mixture of leading tabs and spaces.
The simple rules are: (1) Leading whitespace must consist of tabs only.
(2) Any other whitespace should consist of spaces.
These two rules ensure the integrity of the visual appearance.
Although reformatting existing code should be avoided, I did it.
I did not waste time arguing; I just did it.
.Ci a485ed478abbd599d8c9aab48934e7a26733ecb1

.U3 "Comments
.P
Section 1.6 of
.[ [
kernighan pike practice of programming
.], p. 23]
demands: ``Don't belabor the obvious.''
Hence, I simply removed all the comments in the following code excerpt:
.VS
context_replace(curfolder, folder);  /* update current folder  */
seq_setcur(mp, mp->lowsel);  /* update current message */
seq_save(mp);  /* synchronize message sequences */
folder_free(mp);  /* free folder/message structure */
context_save();  /* save the context file */

[...]

int c;  /* current character */
char *cp;  /* miscellaneous character pointer */

[...]

/* NUL-terminate the field */
*cp = '\0';
VE
.Ci 426543622b377fc5d091455cba685e114b6df674
.P
The names of the functions explain enough already.

.U3 "Names
.P
Kernighan and Pike suggest:
``Use active names for functions''.
.[ [
kernighan pike practice of programming
.], p. 4]
One application of this rule was the rename of
.Fu check_charset()
to
.Fu is_native_charset() .
.Ci 8d77b48284c58c135a6b2787e721597346ab056d
The same change fixed a violation of ``Be accurate'' as well.
The code did not match the expectation the function suggested,
as it, for whatever reason, only compared the first ten characters
of the charset name.
.P
More important than using active names is using descriptive names.
Renaming the obscure function
.Fu m_unknown()
was a delightful event.
.Ci 611d68d19204d7cbf5bd585391249cb5bafca846
.P
Magic numbers are generally considered bad style.
Obviously, Kernighan and Pike agree:
``Give names to magic numbers''.
.[ [
kernighan pike practice of programming
.], p. 19]
One such change was naming the type of input \(en mbox or mail folder \(en
to be scanned:
.VS
#define SCN_MBOX (-1)
#define SCN_FOLD 0
VE
.Ci 7ffb36d28e517a6f3a10272056fc127592ab1c19
.P
The argument
.Ar outnum
of the function
.Fu scan()
in
.Fn uip/scansbr.c
defines the number of the message to be created.
If no message is to be created, the argument is misused to transport
program logic.
This lead to obscure code.
I improved the clarity of the code by introducing two variables:
.VS
int incing = (outnum > 0);
int ismbox = (outnum != 0);
VE
They cover the magic values and are used for conditions.
The variable
.Ar outnum
is only used when it holds an ordinary message number.
.Ci b8b075c77be7794f3ae9ff0e8cedb12b48fd139f
The clarity improvement of the change showed detours in the program logic
of related code parts.
Having the new variables with descriptive names, a more
straight forward implementation became apparent.
Before the clarification was done,
the possibility to improve had not be seen.
.Ci aa60b0ab5e804f8befa890c0a6df0e3143ce0723

.U3 "Rework of \f(CWanno\fP
.P
At the end of their chapter on style,
Kernighan and Pike ask: ``But why worry about style?''
The following example of my rework of
.Pn anno
provides an answer why style is important in the first place.
.P
Until 2002,
.Pn anno
had six functional command line switches,
.Sw -component
and
.Sw -text ,
which took an argument each,
and the two pairs of flags,
.Sw -[no]date
and
.Sw -[no]inplace.,
.Sw -component
and
.Sw -text ,
which took an argument each,
and the two pairs of flags,
.Sw -[no]date
and
.Sw -[no]inplace .
Then Jon Steinhart introduced his attachment system.
In need for more advanced annotation handling, he extended
.Pn anno .
He added five more switches:
.Sw -draft ,
.Sw -list ,
.Sw -delete ,
.Sw -append ,
and
.Sw -number ,
the last one taking an argument.
.Ci 7480dbc14bc90f2d872d434205c0784704213252
Later,
.Sw -[no]preserve
was added.
.Ci d9b1d57351d104d7ec1a5621f090657dcce8cb7f
Then, the Synopsis section of the man page
.Mp anno (1)
read:
.VS
anno [+folder] [msgs] [-component field] [-inplace | -noinplace]
	[-date | -nodate] [-draft] [-append] [-list] [-delete]
	[-number [num|all]] [-preserve | -nopreserve] [-version]
	[-help] [-text body]
VE
.LP
The implementation followed the same structure.
Problems became visible when
.Cl "anno -list -number 42
worked on the current message instead on message number 42,
and
.Cl "anno -list -number l:5
did not work on the last five messages but failed with the mysterious
error message: ``anno: missing argument to -list''.
Yet, the invocation matched the specification in the man page.
There, the correct use of
.Sw -number
was defined as being
.Cl "[-number [num|all]]
and the textual description for the combination with
.Sw -list
read:
.QS
The -list option produces a listing of the field bodies for
header fields with names matching the specified component,
one per line. The listing is numbered, starting at 1, if
the -number option is also used.
.QE
.LP
The problem was manifold.
The code required a numeric argument to the
.Sw -number
switch.
If it was missing or non-numeric,
.Pn anno
aborted with an error message that had an off-by-one error,
printing the switch one before the failing one.
Semantically, the argument to the
.Sw -number
switch is only necessary in combination with
.Sw -delete ,
but not with
.Sw -list .
In the former case it is even necessary.
.P
Trying to fix these problems on the surface would not have solved it truly.
The problems discovered originate from a discrepance between the semantic
structure of the problem and the structure implemented in the program.
Such structural differences can not be cured on the surface.
They need to be solved by adjusting the structure of the implementation
to the structure of the problem.
.P
In 2002, the new switches
.Sw -list
and
.Sw -delete
were added in the same way, the
.Sw -number
switch for instance had been added.
Yet, they are of structural different type.
Semantically,
.Sw -list
and
.Sw -delete
introduce modes of operation.
Historically,
.Pn anno
had only one operation mode: adding header fields.
With the extension, it got two moder modes:
listing and deleting header fields.
The structure of the code changes did not pay respect to this
fundamental change to
.Pn anno 's
behavior.
Neither the implementation nor the documentation did clearly
define them as being exclusive modes of operation.
Having identified the problem, I solved it by putting structure into
.Pn anno
and its documentation.
.Ci d54c8db8bdf01e8381890f7729bc0ef4a055ea11
.P
The difference is visible in both, the code and the documentation.
The following code excerpt:
.VS
int delete = -2;  /* delete header element if set */
int list = 0;  /* list header elements if set */
[...]
	case DELETESW:  /* delete annotations */
		delete = 0;
		continue;
	case LISTSW:  /* produce a listing */
		list = 1;
		continue;
VE
.LP
was replaced by:
.VS
static enum { MODE_ADD, MODE_DEL, MODE_LIST } mode = MODE_ADD;
[...]
	case DELETESW:  /* delete annotations */
		mode = MODE_DEL;
		continue;
	case LISTSW:  /* produce a listing */
		mode = MODE_LIST;
		continue;
VE
.LP
The replacement code does not only reflect the problem's structure better,
it is easier to understand as well.
The same applies to the documentation.
The man page was completely reorganized to propagate the same structure.
This is visible in the Synopsis section:
.VS
anno [+folder] [msgs] [-component field] [-text body]
	[-append] [-date | -nodate] [-preserve | -nopreserve]
	[-Version] [-help]

anno -delete [+folder] [msgs] [-component field] [-text
	body] [-number num | all ] [-preserve | -nopreserve]
	[-Version] [-help]

anno -list [+folder] [msgs] [-component field] [-number]
	[-Version] [-help]
VE
.\" XXX think about explaining the -preserve rework?



.H2 "Standard Libraries
.P
MH is one decade older than the POSIX and ANSI C standards.
Hence, MH included own implementations of functions
that are standardized and thus widely available today,
but were not back then.
Today, twenty years after the POSIX and ANSI C were published,
developers can expect system to comply with these standards.
In consequence, MH-specific replacements for standard functions
can and should be dropped.
Kernighan and Pike advise: ``Use standard libraries.''
.[ [
kernighan pike practice of programming
.], p. 196]
Actually, MH had followed this advice in history,
but it had not adjusted to the changes in this field.
The
.Fu snprintf()
function, for instance, was standardized with C99 and is available
almost everywhere because of its high usefulness.
In project's own implementation of
.Fu snprintf()
was dropped in March 2012 in favor for using the one of the
standard library.
.Ci 0052f1024deb0a0a2fc2e5bacf93d45a5a9c9b32
Such decisions limit the portability of mmh
if systems don't support these standardized and widespread functions.
This compromise is made because mmh focuses on the future.
.P
I am not yet thirty years old and my C and Unix experience comprises
only half a dozen years.
Hence, I need to learn about the history in retrospective.
I have not used those ancient constructs myself.
I have not suffered from their incompatibilities.
I have not longed for standardization.
All my programming experience is from a time when ANSI C and POSIX
were well established already.
I have only read a lot of books about the (good) old times.
This puts me in a difficult positions when working with old code.
I need to freshly acquire knowledge about old code constructs and ancient
programming styles, whereas older programmers know these things by
heart from their own experience.
.P
Being aware of the situation, I rather let people with more historic
experience replace ancient code constructs with standardized ones.
Lyndon Nerenberg covered large parts of this task for the nmh project.
He converted project-specific functions to POSIX replacements,
also removing the conditionals compilation of now standardized features.
Ken Hornstein and David Levine had their part in the work, too.
Often, I only needed to pull over changes from nmh into mmh.
These changes include many commits; these are among them:
.Ci 768b5edd9623b7238e12ec8dfc409b82a1ed9e2d
.Ci 0052f1024deb0a0a2fc2e5bacf93d45a5a9c9b32 .
.P
During my own work, I tidied up the \fIMH standard library\fP,
.Fn libmh.a ,
which is located in the
.Fn sbr
(``subroutines'') directory in the source tree.
The MH library includes functions that mmh tools usually need.
Among them are MH-specific functions for profile, context, sequence,
and folder handling, but as well
MH-independent functions, such as auxiliary string functions,
portability interfaces and error-checking wrappers for critical
functions of the standard library.
.P
I have replaced the
.Fu atooi()
function with calls to
.Fu strtoul()
with the third parameter \(en the base \(en set to eight.
.Fu strtoul()
is part of C89 and thus considered safe to use.
.Ci c490c51b3c0f8871b6953bd0c74551404f840a74
.P
I did remove project-included fallback implementations of
.Fu memmove()
and
.Fu strerror() ,
although Peter Maydell had re-included them into nmh in 2008
to support SunOS 4.
Nevertheless, these functions are part of ANSI C.
Systems that do not even provide full ANSI C support should not
put a load on mmh.
.Ci b067ff5c465a5d243ce5a19e562085a9a1a97215
.P
The
.Fu copy()
function copies the string in argument one to the location in two.
In contrast to
.Fu strcpy() ,
it returns a pointer to the terminating null-byte in the destination area.
The code was adjusted to replace
.Fu copy()
with
.Fu strcpy() ,
except within
.Fu concat() ,
where
.Fu copy()
was more convenient.
Therefore, the definition of
.Fu copy()
was moved into the source file of
.Fu concat()
and its visibility is now limited to it.
.Ci 552fd7253e5ee9e554c5c7a8248a6322aa4363bb
.P
The function
.Fu r1bindex()
had been a generalized version of
.Fu basename()
with minor differences.
As all calls to
.Fu r1bindex()
had the slash (`/') as delimiter anyway,
replacing
.Fu r1bindex()
with the more specific and better-named function
.Fu basename()
became desirable.
Unfortunately, many of the 54 calls to
.Fu r1bindex()
depended on a special behavior,
which differed from the POSIX specification for
.Fu basename() .
Hence,
.Fu r1bindex()
was kept but renamed to
.Fu mhbasename() ,
fixing the delimiter to the slash.
.Ci 240013872c392fe644bd4f79382d9f5314b4ea60
For possible uses of
.Fu r1bindex()
with a different delimiter,
the ANSI C function
.Fu strrchr()
provides the core functionality.
.P
The
.Fu ssequal()
function \(en apparently for ``substring equal'' \(en
was renamed to
.Fu isprefix() ,
because this is what it actually checks.
.Ci c20b4fa14515c7ab388ce35411d89a7a92300711
Its source file had included the following comments, no joke.
.VS
/*
 * THIS CODE DOES NOT WORK AS ADVERTISED.
 * It is actually checking if s1 is a PREFIX of s2.
 * All calls to this function need to be checked to see
 * if that needs to be changed. Prefix checking is cheaper, so
 * should be kept if it's sufficient.
 */

/*
 * Check if s1 is a substring of s2.
 * If yes, then return 1, else return 0.
 */
VE
Two months later, it was completely removed by replacing it with
.Fu strncmp() .
.Ci b0b1dd37ff515578cf7cba51625189eb34a196cb





.H2 "Modularization
.P
The source code of the mmh tools is located in the
.Fn uip
(``user interface programs'') directory.
Each tools has a source file with the same name.
For example,
.Pn rmm
is built from
.Fn uip/rmm.c .
Some source files are used for multiple programs.
For example
.Fn uip/scansbr.c
is used for both,
.Pn scan
and
.Pn inc .
In nmh, 49 tools were built from 76 source files.
This is a ratio of 1.6 source files per program.
32 programs depended on multiple source files;
17 programs depended on one source file only.
In mmh, 39 tools are built from 51 source files.
This is a ratio of 1.3 source files per program.
18 programs depend on multiple source files;
21 programs depend on one source file only.
(These numbers and the ones in the following text ignore the MH library
as well as shell scripts and multiple names for the same program.)
.P
Splitting the source code of a large program into multiple files can
increase the readability of its source code.
Most of the mmh tools, however, are simple and straight-forward programs.
With the exception of the MIME handling tools,
.Pn pick
is the largest tools.
It contains 1\|037 lines of source code (measured with
.Pn sloccount ), excluding the MH library.
Only the MIME handling tools (\c
.Pn mhbuild ,
.Pn mhstore ,
.Pn show ,
etc.)
are larger.
Splitting programs with less than 1\|000 lines of code into multiple
source files seldom leads to better readability.
For such tools, splitting makes sense
when parts of the code are reused in other programs,
and the reused code fragment is not general enough
for including it in the MH library,
or, if the code has dependencies on a library that only few programs need.
.Fn uip/packsbr.c ,
for instance, provides the core program logic for the
.Pn packf
and
.Pn rcvpack
programs.
.Fn uip/packf.c
and
.Fn uip/rcvpack.c
mainly wrap the core function appropriately.
No other tools use the folder packing functions.
As another example,
.Fn uip/termsbr.c
provides termcap support, which requires linking with a termcap or
curses library.
Including
.Fn uip/termsbr.c
into the MH library would require every program to be linked with
termcap or curses, although only few of the programs require it.
.P
The task of MIME handling is complex enough that splitting its code
into multiple source files improves the readability.
The program
.Pn mhstore ,
for instance, is compiled out of seven source files with 2\|500
lines of code in summary.
The main code file
.Fn uip/mhstore.c
consists of 800 lines; the other 1\|700 lines of code are reused in
other MIME handling tools.
It seems to be worthwhile to bundle the generic MIME handling code into
a MH-MIME library, as a companion to the MH standard library.
This is left open for the future.
.P
The work already done, focussed on the non-MIME tools.
The amount of code compiled into each program was reduced.
This eases the understanding of the code base.
In nmh,
.Pn comp
was built from six source files:
.Fn comp.c ,
.Fn whatnowproc.c ,
.Fn whatnowsbr.c ,
.Fn sendsbr.c ,
.Fn annosbr.c ,
and
.Fn distsbr.c .
In mmh, it builds from only two:
.Fn comp.c
and
.Fn whatnowproc.c .
In nmh's
.Pn comp ,
the core function of
.Pn whatnow ,
.Pn send ,
and
.Pn anno
were compiled into
.Pn comp .
This saved the need to execute these programs with
.Fu fork()
and
.Fu exec() ,
two expensive system calls.
Whereis this approach improved the time performance,
it interweaved the source code.
Core functionalities were not encapsulated into programs but into
function, which were then wrapped by programs.
For example,
.Fn uip/annosbr.c
included the function
.Fu annotate() .
Each program that wanted to annotate messages, included the source file
.Fn uip/annosbr.c
and called
.Fu annotate() .
Because the function
.Fu annotate()
was used like the tool
.Pn anno ,
it had seven parameters, reflecting the command line switches of the tool.
When another pair of command line switches was added to
.Pn anno ,
a rather ugly hack was implemented to avoid adding another parameter
to the function.
.Ci d9b1d57351d104d7ec1a5621f090657dcce8cb7f
.P
Separation simplifies the understanding of program code
because the area influenced by any particular statement is smaller.
The separating on the program-level is more strict than the separation
on the function level.
In mmh, the relevant code of
.Pn comp
comprises the two files
.Fn uip/comp.c
and
.Fn uip/whatnowproc.c ,
together 210 lines of code.
In nmh,
.Pn comp
comprises six files with 2\|450 lines.
Not all of the code in these six files was actually used by
.Pn comp ,
but the code reader needed to read all of the code first to know which
parts were used.
.P
As I have read a lot in the code base during the last two years,
I learned about the easy and the difficult parts.
Code is easy to understand if:
.BU
The influenced code area is small
.BU
The boundaries are strictly defined
.BU
The code is written straight-forward
.P
.\" XXX move this paragraph somewhere else?
Reading
.Pn rmm 's
source code in
.Fn uip/rmm.c
is my recommendation for a beginner's entry point into the code base of nmh.
The reasons are that the task of
.Pn rmm
is straight forward and it consists of one small source code file only,
yet its source includes code constructs typical for MH tools.
With the introduction of the trash folder in mmh,
.Pn rmm
became a bit more complex, because it invokes
.Pn refile .
Still, it is a good example for a simple tool with clear sources.
.P
Understanding
.Pn comp
requires to read 210 lines of code in mmh, but ten times as much in nmh.
Due to the aforementioned hack in
.Pn anno
to save the additional parameter, information passed through the program's
source base in obscure ways.
Thus, understanding
.Pn comp ,
required understanding the inner workings of
.Fn uip/annosbr.c
first.
To be sure to fully understand a program, its whole source code needs
to be examined.
Not doing so is a leap of faith, assuming that the developers
have avoided obscure programming techniques.
By separating the tools on the program-level, the boundaries are
clearly visible and technically enforced.
The interfaces are calls to
.Fu exec()
rather than arbitrary function calls.
.P
But the real problem is another:
Nmh violates the golden ``one tool, one job'' rule of the Unix philosophy.
Understanding
.Pn comp
requires understanding
.Fn uip/annosbr.c
and
.Fn uip/sendsbr.c
because
.Pn comp
does annotate and send messages.
In nmh, there surely exists the tool
.Pn send ,
which does (almost) only send messages.
But
.Pn comp
and
.Pn repl
and
.Pn forw
and
.Pn dist
and
.Pn whatnow
and
.Pn viamail ,
they all (!) have the same message sending function included, too.
In result,
.Pn comp
sends messages without using
.Pn send .
The situation is the same as if
.Pn grep
would page without
.Pn more
just because both programs are part of the same code base.
.P
The clear separation on the surface \(en the toolchest approach \(en
is violated on the level below.
This violation is for the sake of time performance.
On systems where
.Fu fork()
and
.Fu exec()
are expensive, the quicker response might be noticable.
In the old times, sacrificing readability and conceptional beauty for
speed might even have been a must to prevent MH from being unusably slow.
Whatever the reasons had been, today they are gone.
No longer should we sacrifice readability or conceptional beauty.
No longer should we violate the Unix philosophy's ``one tool, one job''
guideline.
No longer should we keep speed improvements that became unnecessary.
.P
Therefore, mmh's
.Pn comp
does no longer send messages.
In mmh, different jobs are divided among separate programs that
invoke each other as needed.
In consequence,
.Pn comp
invokes
.Pn whatnow
which thereafter invokes
.Pn send .
The clear separation on the surface is maintained on the level below.
Human users and the tools use the same interface \(en
annotations, for example, are made by invoking
.Pn anno ,
no matter if requested by programs or by human beings.
The decrease of tools built from multiple source files and thus
the decrease of
.Fn uip/*sbr.c
files confirm the improvement.
.P
One disadvantage needs to be taken with this change:
The compiler can no longer check the integrity of the interfaces.
By changing the command line interfaces of tools, it is
the developer's job to adjust the invocations of these tools as well.
As this is a manual task and regression tests, which could detect such
problems, are not available yet, it is prone to errors.
These errors will not be detected at compile time but at run time.
Installing regression tests is a task left to do.
In the best case, a uniform way of invoking tools from other tools
can be developed to allow automated testing at compile time.




.H2 "User Data Locations
.P
In nmh, a personal setup consists of the MH profile and the MH directory.
The profile is a file named
.Fn \&.mh_profile
in the user's home directory.
It contains the static configuration.
It also contains the location of the MH directory in the profile entry
.Pe Path .
The MH directory contains the mail storage and is the first
place to search for personal forms, scan formats, and similar
configuration files.
The location of the MH directory can be chosen freely by the user.
The default and usual name is a directory named
.Fn Mail
in the home directory.
.P
The way MH data is splitted between profile and MH directory is a legacy.
It is only sensible in a situation where the profile is the only
configuration file.
Why else should the mail storage and the configuration files be intermixed?
They are different kinds of data:
The data to be operated on and the configuration to change how
tools operate.
Splitting the configuration between the profile and the MH directory
is bad.
Merging the mail storage and the configuration in one directory is bad
as well.
As the mail storage and the configuration were not separated sensibly
in the first place, I did it now.
.P
Personal mmh data is grouped by type, resulting in two distinct parts:
The mail storage and the configuration.
In mmh, the mail storage directory still contains all the messages,
but, in exception of public sequences files, nothing else.
In difference to nmh, the auxiliary configuration files are no longer
located there.
Therefore, the directory is no longer called the user's \fIMH directory\fP
but his \fImail storage\fP.
Its location is still user-chosen, with the default name
.Fn Mail ,
in the user's home directory.
In mmh, the configuration is grouped together in
the hidden directory
.Fn \&.mmh
in the user's home directory.
This \fImmh directory\fP contains the context file, personal forms,
scan formats, and the like, but also the user's profile, now named
.Fn profile .
The location of the profile is no longer fixed to
.Fn $HOME/.mh_profile
but to
.Fn $HOME/.mmh/profile .
Having both, the file
.Fn $HOME/.mh_profile
and the configuration directory
.Fn $HOME/.mmh
appeared to be inconsistent.
The approach chosen for mmh is consistent, simple, and familiar to
Unix users.
.P
MH allows users to have multiiple MH setups.
Therefore, it is necessary to select a different profile.
The profile is the single entry point to access the rest of a
personal MH setup.
In nmh, the environment variable
.Ev MH
could be used to specifiy a different profile.
To operate in the same MH setup with a separate context,
the
.Ev MHCONTEXT
environment variable could be used.
This allows having own current folders and current messages in
each terminal, for instance.
In mmh, three environment variables are used.
.Ev MMH
overrides the default location of the mmh directory (\c
.Fn .mmh ).
.Ev MMHP
and
.Ev MMHC
override the paths to the profile and context files, respectively.
This approach allows the set of personal configuration files to be chosen
independently from the profile, context, and mail storage.
.P
The separation of the files by type is sensible and convenient.
The new approach has no functional disadvantages,
as every setup I can imagine can be implemented with both approaches,
possibly even easier with the new approach.
The main achievement of the change is the clear and sensible split
between mail storage and configuration.






.H1 "Concept Exploitation/Homogeneity


.H2 "Draft Folder
.P
Historically, MH provided exactly one draft message, named
.Fn draft
and
being located in the MH directory.
When starting to compose another message
before the former one was sent, the user had been questioned whether to use,
refile or replace the old draft.
Working on multiple drafts at the same time
was impossible.
One could only work on them in alteration by refiling the
previous one to some directory and fetching some other one for reediting.
This manual draft management needed to be done each time the user wanted
to switch between editing one draft to editing another.
.P
To allow true parallel editing of drafts, in a straight forward way, the
draft folder facility exists.
It had been introduced already in July 1984
by Marshall T. Rose.
The facility was inactive by default.
Even in nmh, the draft folder facility remained inactive by default.
At least, Richard Coleman added the man page
.Mp mh-draft(5)
to document
the feature well.
.P
The only advantage of not using the draft folder facility is the static
name of the draft file.
This could be an issue for MH front-ends like mh-e.
But as they likely want to provide working on multiple drafts in parallel,
the issue is only concerning compatibility.
The aim of nmh to stay compatible
prevented the default activation of the draft folder facility.
.P
On the other hand, a draft folder is the much more natural concept than
a draft message.
MH's mail storage consists of folders and messages,
the messages named with ascending numbers.
A draft message breaks with this
concept by introducing a message in a file named
.Fn draft .
This draft
message is special.
It can not be simply listed with the available tools,
but instead requires special switches.
I.e. corner-cases were
introduced.
A draft folder, in contrast, does not introduce such
corner-cases.
The available tools can operate on the messages within that
folder like on any messages within any mail folders.
The only difference
is the fact that the default folder for
.Pn send
is the draft folder,
instead of the current folder, like for all other tools.
.P
The trivial part of the change was activating the draft folder facility
by default and setting a default name for this folder.
Obviously, I chose
the name
.Fn +drafts .
This made the
.Sw -draftfolder
and
.Sw -draftmessage
switches useless, and I could remove them.
The more difficult but also the part that showed the real improvement,
was updating the tools to the new concept.
.Sw -draft
switches could
be dropped, as operating on a draft message became indistinguishable to
operating on any other message for the tools.
.Pn comp
still has its
.Sw -use
switch for switching between its two modes: (1) Compose a new
draft, possibly by taking some existing message as a form.
(2) Modify
an existing draft.
In either case, the behavior of
.Pn comp is
deterministic.
There is no more need to query the user.
I consider this
a major improvement.
By making
.Pn send
simply operate on the current
message in the draft folder by default, with message and folder both
overridable by specifying them on the command line, it is now possible
to send a draft anywhere within the storage by simply specifying its folder
and name.
.P
All theses changes converted special cases to regular cases, thus
simplifying the tools and increasing the flexibility.


.H2 "Trash Folder
.P
Similar to the situation for drafts is the situation for removed messages.
Historically, a message was deleted by renaming.
A specific
\fIbackup prefix\fP, often comma (\c
.Fn , )
or hash (\c
.Fn # ),
being prepended to the file name.
Thus, MH wouldn't recognize the file
as a message anymore, as only files whose name consists of digits only
are treated as messages.
The removed messages remained as files in the
same directory and needed some maintenance job to truly delete them after
some grace time.
Usually, by running a command similar to
.VS
find /home/user/Mail -ctime +7 -name ',*' | xargs rm
VE
in a cron job.
Within the grace time interval
the original message could be restored by stripping the
the backup prefix from the file name.
If however, the last message of
a folder is been removed \(en say message
.Fn 6
becomes file
.Fn ,6
\(en and a new message enters the same folder, thus the same
numbered being given again \(en in our case
.Fn 6
\(en, if that one
is removed too, then the backup of the former message gets overwritten.
Thus, the ability to restore removed messages does not only depend on
the ``sweeping cron job'' but also on the removing of further messages.
This is undesirable, because the real mechanism is hidden from the user
and the consequences of further removals are not always obvious.
Further more, the backup files are scattered within the whole mail
storage, instead of being collected at one place.
.P
To improve the situation, the profile entry
.Pe rmmproc
(previously named
.Pe Delete-Prog )
was introduced, very early.
It could be set to any command, which would care for the mail removal
instead of taking the default action, described above.
Refiling the to-be-removed files to some garbage folder was a common
example.
Nmh's man page
.Mp rmm(1)
proposes
.Cl "refile +d
to move messages to the garbage folder and
.Cl "rm `mhpath +d all`
the empty the garbage folder.
Managing the message removal this way is a sane approach.
It keeps
the removed messages in one place, makes it easy to remove the backup
files, and, most important, enables the user to use the tools of MH
itself to operate on the removed messages.
One can
.Pn scan
them,
.Pn show
them, and restore them with
.Pn refile .
There's no more
need to use
.Pn mhpath
to switch over from MH tools to Unix tools \(en MH can do it all itself.
.P
This approach matches perfect with the concepts of MH, thus making
it powerful.
Hence, I made it the default.
And even more, I also
removed the old backup prefix approach, as it is clearly less powerful.
Keeping unused alternative in the code is a bad choice as they likely
gather bugs, by not being constantly tested.
Also, the increased code
size and more conditions crease the maintenance costs.
By strictly
converting to the trash folder approach, I simplified the code base.
.Pn rmm
calls
.Pn refile
internally to move the to-be-removed
message to the trash folder (\c
.Fn +trash
by default).
Messages
there can be operated on like on any other message in the storage.
The sweep clean, one can use
.Cl "rmm -unlink +trash a" ,
where the
.Sw -unlink
switch causes the files to be truly unliked instead
of moved to the trash folder.


.H2 "Path Notations
.P
foo


.H2 "MIME Integration
.P
user-visible access to whole messages and MIME parts are inherently
different


.H2 "Of One Cast
.P