docs/diploma

annotate thesis/tex/4-MasqmailsFuture.tex @ 169:fa086dbbdf10

find changesets by author, revision, files, or words in the commit message
split cover from main document
author meillo@marmaro.de
date Fri, 19 Dec 2008 23:35:38 +0100
parents 4ac06b7b9bdf
children 204683bfb4e7
rev   line source
meillo@109 1 \chapter{\masqmail's present and future}
meillo@93 2
meillo@137 3 \section{Existing code base}
meillo@142 4 Here regarded is version 0.2.21 of \masqmail. This is the last version released by Oliver \person{Kurth}, and the basis for my thesis.
meillo@142 5
meillo@93 6
meillo@137 7 \subsubsection*{Features}
meillo@93 8
meillo@142 9 \masqmail\ accepts mail on the command line and via \SMTP. Mail queueing and alias expansion is supported. \masqmail\ is able to deliver mail to local mailboxes (in \name{mbox} or \name{maildir} format) or pass it to a \name{mail delivery agent} (like \name{procmail}). Mail destinated to remote locations is sent using \SMTP\ or can be piped to commands, being gatesways to \NAME{UUCP} or \NAME{FAX} for example.
meillo@93 10
meillo@142 11 Outgoing \SMTP\ connections feature \SMTP-\NAME{AUTH} and \SMTP-after-\NAME{POP} authentication, but incoming connections do not. Using wrappers for outgoing connections is supported. This offers a two way communication through a wrapper application like \name{openssl}.
meillo@137 12 %todo: what about SSL/TLS encryption?
meillo@93 13
meillo@142 14 \masqmail\ focuses on non-permanent online connections, thus a concept of online routes is used. One may configure any amount of routes to send mail. Each route can have criterias, like matching \texttt{From:} or \texttt{To:} headers, to determine if mail is allowed to be sent using it. Mail to destinations outside the local net gets queued until \masqmail\ is informed about the existance of a online connection.
meillo@142 15
meillo@137 16 The \masqmail\ executable can be called under various names for sendmail-compatibility reasons. This is organized by symbolic links with different names pointing to the \masqmail\ executable. The \sendmail\ names are \path{/usr/lib/sendmail} and \path{/usr/sbin/sendmail} because many programs expect the \mta\ to be located there. Further more \sendmail\ supports calling it with a different name instead of supplying command line arguments. The best known of this shortcuts is \path{mailq}, which is equivilent to calling it with the argument \verb+-bq+. \masqmail\ recognizes the names \path{mailq}, \path{smtpd}, \path{mailrm}, \path{runq}, \path{rmail}, and \path{in.smtpd}. The first two are inspired by \sendmail. Not implemented is the name \path{newaliases} because \masqmail\ does not generate binary representations of the alias file.\footnote{A shell script located named \path{newaliases}, that invokes \texttt{masqmail -bi}, can provide the command to satisfy other software needing it.} \path{hoststat} and \path{purgestat} are missing for sendmail-compatibility.
meillo@109 17 %masqmail: mailq, mailrm, runq, rmail, smtpd/in.smtpd
meillo@109 18 %sendmail: hoststat, mailq, newaliases, purgestat, smtpd
meillo@109 19
meillo@137 20 Additional to the \mta\ job, \masqmail\ also offers mail retrieval services with being a \NAME{POP3} client. It can fetch mail from different remote locations, dependent on the active online route.
meillo@109 21
meillo@137 22
meillo@137 23
meillo@137 24 \subsubsection*{The code}
meillo@137 25
meillo@137 26 \masqmail\ is written in the C programming language. The program, as of version 0.2.21, consists of 34 source code and eight header files, containing about 9,000 lines of code\footnote{Measured with \name{sloccount} by David A.\ Wheeler.}. Additionally, it includes a \name{base64} implementation (about 300 lines) and \name{md5} code (about 150 lines). For systems that do not provide \name{libident}, this library is distributed as well (circa 600 lines); an available shared library however has higher precedence in linking.
meillo@137 27
meillo@137 28 The only mandatory dependency is \name{glib}---a cross-platform software utility library, originated in the \NAME{GTK+} project. It provides safer replacements for many standard library functions. It also offers handy data containers, easy-to-use implementations of data structures, and much more.
meillo@137 29
meillo@109 30
meillo@109 31 With \masqmail\ comes the small tool \path{mservdetect}; it helps setting up a configuration that uses the \name{mserver} system to detect the online state. Two other binaries get compiled for testing purposes: \path{readtest} and \path{smtpsend}. All three programms use \masqmail\ source code; they only add a file with a \verb+main()+ function each.
meillo@109 32
meillo@93 33
meillo@137 34 \masqmail\ does not provide an interface to plug in modules with additional functionality. There exists no add-on or module system. The code is only separated by function to the various source files. Some functional parts can be included or excluded by defining symbols. Adding maildir support at compile time, means giving the option \verb+--enable-maildir+ to the \path{configure} call. This preserves the concerning code to get removed by the preprocessor. Unfortunately the \verb+#ifdef+s are scattered through all the source, leading to a FIXME(holperig) code base.
meillo@93 35
meillo@132 36
meillo@132 37
meillo@132 38
meillo@132 39
meillo@146 40
meillo@146 41 \section{Requirements}
meillo@146 42
meillo@146 43 Following is a list of current and future requirements to make \masqmail\ ready for the future.
meillo@146 44
meillo@146 45
meillo@146 46 \subsubsection*{Large message handling}
meillo@155 47 Trends in the market for electronic communication go towards consolidated communication, hence email will be used more to transfer voice and video messages. This leads to larger messages. The store-and-forward transport of email is not good suited for large data. Thus new protocols, like \NAME{QMTP} (described in section %\ref{FIXME}
meillo@155 48 ), may become popular.
meillo@146 49
meillo@146 50
meillo@146 51 \subsubsection*{Ressource friendly software}
meillo@149 52 The merge of communication hardware and the move of email services from providers to homes, demands smaller and more resource-friendly software. The amount of mail will be lower, even if much more mail will be sent. More important will be the energy consumption and heat emission. These topics increased in relevance during the past years and they are expected to become more central. \masqmail\ is not a program to be used on large servers, but to be used on small devices. Thus focusing on energy and heat, not on performance, is the direction to go.
meillo@146 53
meillo@146 54
meillo@146 55 \subsubsection*{New mail transfer protocols}
meillo@149 56 Large messages demand more efficient transport through the net. As well is a final solution needed to defeat the spam problem. New mail transport protocols may be the only good solutions for both problems. They also can improve reliability, authentication, and verification issues. \masqmail\ should be able to support new protocols as they appear and are used.
meillo@146 57
meillo@146 58
meillo@149 59 \subsubsection*{Spam handling}
meillo@149 60 Spam is a major threat. According to the \NAME{SWOT} analysis, the goal is to reduce it to a bearable level. Spam fighting is a war are where the good guys tend to lose. Putting too much effort there will result in few gain. Real success will only be possible with new---better---protocols and abandonning the weak legacy technologies. Hence \masqmail\ should be able to provide state-of-the-art spam protection, but not more.
meillo@146 61
meillo@146 62
meillo@161 63 \subsubsection*{Security}
meillo@161 64 \MTA{}s are critical points for computer security, as they are accessable from external networks. They must be secured with high effort. Properties like high priviledge level, work load influenced from extern, work on unsafe data, and demand for reliability, increase the security needed. Unsecure and unreliable \mta{}s are of no value. \masqmail\ needs to b e secure enough for its target field of operation.
meillo@161 65
meillo@161 66
meillo@146 67 \subsubsection*{Easy configuration}
meillo@149 68 Having \mta{}s on many home servers and clients, requires easy and standardized configuration. The common setups should be configurable with single actions by the user. Complex configuration should be possible, but focused must be the most common form of configuration: choosing one of several standard setups.
meillo@146 69
meillo@146 70
meillo@146 71
meillo@146 72
meillo@146 73
meillo@146 74
meillo@161 75 \section{Discussion on architecture}
meillo@146 76
meillo@163 77 A program's architecture is probably the most influencing design decision, and has the greatest impact on the program's future capabilities. %fixme: search quote ... check if good
meillo@132 78
meillo@161 79 \masqmail's current artitecture is monolitic like \sendmail's and \exim's. But more than the other two, is it one block of interweaved code. \sendmail\ provides now, with its \name{milter} interface, standardized connection channels to external modules. \exim\ has a highly structured code with many internal interfaces, like the one for supported authentication ``modules''. \masqmail\ has none of them; it is what \sendmail\ was in the beginning: a single large block.
meillo@161 80
meillo@161 81 Figure \ref{fig:masqmail-arch} is an attempt to depict \masqmail's internal structure.
meillo@161 82
meillo@161 83 \begin{figure}
meillo@161 84 \begin{center}
meillo@161 85 \input{input/masqmail-arch.tex}
meillo@161 86 \end{center}
meillo@161 87 \caption{Internal architecture of \masqmail}
meillo@161 88 \label{fig:masqmail-arch}
meillo@161 89 \end{figure}
meillo@161 90
meillo@163 91 \sendmail\ improved its old architecture, for example by adding the milter interface. \exim\ was designed and is carefully maintained with a modular-like code structure in mind. \qmail\ started from scratch with a ``security-first'' approach, \postfix\ improved on it, and \name{sendmail X}/\name{MeTA1} tries to adopt the best of \qmail\ and \postfix, to completely replace the old \sendmail\ architecture. \person{Hafiz} \cite{hafiz05}. describes this evolution of \mta\ architecture very well.
meillo@161 92
meillo@163 93 Every one of the popular \MTA{}s is more modular, or became more modular over time, than \masqmail\ is. Modern requirements like spam protection and future requirements like the use of new mail transport protocols demand modular designs for keeping the software simple. Simplicity is a key property for security.
meillo@161 94
meillo@163 95 \person{Hafiz} agrees:
meillo@163 96 \begin{quote}
meillo@163 97 The goal of making software secure can be better achieved by making the design simple and easier to understand and verify. \cite[page64]{hafiz05}
meillo@163 98 \end{quote}
meillo@163 99 He identifies the security of \qmail\ to come from it's \name{compartmentalization}, which goes hand in hand with modularity:
meillo@163 100 \begin{quote}
meillo@163 101 A perfect example is the contrast between the feature envy early \sendmail\ architecture implemented as one process and the simple, modular architecture of \qmail. The security of \qmail\ comes from its compartmentalized simple processes that perform one task only and are therefor testable for security. \cite[page 64]{hafiz05}
meillo@163 102 \end{quote}
meillo@165 103 As well does \person{Dent}: ``The modular architecture of Postfix forms the basis for much of its security.''\cite[page 7]{dent04}
meillo@161 104
meillo@163 105 Modularity is needed for supporting modern \MTA\ requirements, providing a clear interface to add further functionality without increasing the overall complexity much. Modularity is also an enabler for security. Security comes from good design, as \person{Graff} and \person{van Wyk} explain:
meillo@163 106 \begin{quote}
meillo@163 107 Good design is the sword and shield of the security-conscious developer. Sound design defends your application from subversion or misuse, protecting your network and the information on it from internal and external attacks alike. It also provides a safe foundation for future extensions and maintainance of the software.
meillo@163 108 %
meillo@163 109 %Bad design makes life easier for attackers and harder for the good guys, especially if it contributes to a false sends of security while obscuring pertinent failings.
meillo@163 110 \cite[page 55]{graff03}
meillo@163 111 \end{quote}
meillo@161 112
meillo@163 113 \person{Hafiz} adds: ``The major idea is that security cannot be retrofitted into an architecture.''\cite[page 64]{hafiz05}
meillo@161 114
meillo@163 115 All this leads to one logical step: The rewrite of \masqmail\ using a modern, modular architecture, to get a modern \MTA\ satisfying nowadays needs.
meillo@161 116
meillo@161 117
meillo@161 118
meillo@161 119
meillo@163 120 \subsection{Modules needed}
meillo@161 121
meillo@163 122 This section tries to identify the needed modules for a modern \MTA. They are later the pieces of which the new architecture is built of.
meillo@163 123
meillo@163 124
meillo@165 125 \subsubsection*{The simple view}
meillo@163 126
meillo@165 127 The basic job of a \mta\ is to tranport mail from a sender to a recipient. This is the definition of such a program and this is how \person{Dent}\cite[page 19]{dent04} and \person{Hafiz} \cite[pages 3-5]{hafiz05} start on the design.
meillo@163 128
meillo@165 129 An \MTA\ therefor needs at least a mail receiving facility and a mail sending facility. But both, and probably all \MTA\ developers (excluded the only forwarders), see the need for a mail queue. A mail queue removed the need to deliver at once. They also provide fail-safe storage of mails until they are delivered.
meillo@163 130
meillo@163 131
meillo@163 132
meillo@163 133
meillo@163 134 \subsubsection*{Incoming channels}
meillo@163 135
meillo@163 136 The second addition \person{Hafiz} made is the split of incoming and outgoing channels into local and remote. The question is, if this is nessesary. It is the way, it was done for a long time, but is this extra complexity needed?
meillo@163 137
meillo@163 138 The common situation is incoming mail on port 25 using \SMTP\ and via the \texttt{sendmail} command. Outgoing mail is either sent using \SMTP, piped into local commands (for example \texttt{uucp}), or delivered locally by appending to a mailbox.
meillo@163 139
meillo@163 140 The \MTA's architecture would be simpler if some of these channels could be merged. The reason is, if various modules do similar jobs, common things might need to be duplicated. On the other side is it better to have more independent modules if each one is simpler then.
meillo@163 141
meillo@163 142 \qmail\ uses \name{qmail-inject} (local message in) and \name{qmail-smtpd} (remote message in), which both handle messages over to \name{qmail-queue} that puts it into the mail queue. \postfix's approach is similar. \name{sendmail X} %fixme: what about meta1 here?
meillo@163 143 used only \NAME{SMTPS}, which is for receiving mail from remote, to communicate with the queue manager \NAME{QMGR}. Mail from local goes over \NAME{SMTPS}.
meillo@163 144
meillo@163 145 The \name{sendmail X} approach seems to be the simpler one, but does heavily rely on \SMTP\ being the main mail transfer protocol. To \qmail\ and \postfix\ new modules may be added to support other ways of message receival, without any change of other parts of the system.
meillo@163 146
meillo@163 147
meillo@163 148 \subsubsection*{Outgoing channels}
meillo@163 149
meillo@163 150 Outgoing channels are similar for \qmail, \postfix, and \name{sendmail X}: All of them have a module to send mail using \SMTP, and one for writing into a local mailbox. Local mail delivery is a job that requires root priveledge to be able to switch to any user in order to write to his mailbox. Modular \MTA{}s do not need \name{setuid root}, but the local delivery process (or its parent) needs to run as root.
meillo@163 151
meillo@163 152 As mail delivery to local users, is \emph{not} included in the basic job of \MTA{}s, why should they care about it? In order to keep the system simple and to have programs do one job well, the local delivery job should be handed over to \NAME{MDA}s. \name{Mail delivery agents} are the tools that are specialized for local delivery. They know about the various mailbox formats and are aware of the problems of concurrent write access and thelike. Hence handling the message and the responsiblity for it over to a mail delivery agent, like \name{procmail} or \name{maildrop}, seems to be the right way to go.
meillo@163 153
meillo@163 154 This means outgoing connections, piping mails into local commands needs to be implemented.
meillo@163 155
meillo@163 156
meillo@165 157
meillo@165 158 \subsubsection*{Sanitize mail}
meillo@165 159 generate valid headers: add, rewrite
meillo@165 160 ... better before inserting into the queue
meillo@165 161
meillo@165 162 (determine the method to send at that position?)
meillo@165 163
meillo@165 164
meillo@165 165
meillo@165 166
meillo@165 167 \subsubsection*{Aliasing}
meillo@165 168
meillo@165 169 where to expand aliases?
meillo@165 170
meillo@165 171
meillo@165 172
meillo@165 173 \subsubsection*{Mail queue}
meillo@165 174
meillo@165 175 Mail queues are probably used in all \mta{}s, excluding the simple forwarders. A mail queue is a essential requirement for \masqmail, as it is to be used for non-permanent online connections.
meillo@165 176
meillo@165 177
meillo@165 178
meillo@163 179
meillo@163 180
meillo@163 181
meillo@163 182
meillo@163 183 \subsubsection*{Authentication}
meillo@163 184
meillo@165 185 either by
meillo@165 186 - network/ip address
meillo@165 187 easiest: restricting by static IP addresses (Access control via hosts.allow/hosts.deny)
meillo@165 188 or
meillo@165 189 - some kind of auth (for dynamic remote hosts)
meillo@165 190 adds complexity
meillo@165 191 - SASL
meillo@165 192 - POP/IMAP: pop-before-smtp, DRAC, WHOSON
meillo@165 193 - TLS (certificates)
meillo@163 194
meillo@165 195 \begin{quote}
meillo@165 196 None of these add-ons is an ideal solution. They require additional code compiled into your existing daemons that may then require special write accesss to system files. They also require additional work for busy system administrators. If you cannot use any of the nonauthenticating alternatives mentioned earlier, or your business requirements demand that all of thyour users' mail pass through your system no matter where they are on the Internet, SASL is probably the solution that offers the most reliable and scalable method to authenticate users.
meillo@165 197 \cite[page 44]{dent04}
meillo@165 198 \end{quote}
meillo@163 199
meillo@163 200
meillo@163 201 \subsubsection*{Encryption}
meillo@163 202
meillo@165 203 TLS/SSL prevents attackers to listen on the cable
meillo@165 204 but it does not prevent man-in-the-middle attacks
meillo@165 205 signed certificates help here
meillo@165 206
meillo@165 207
meillo@165 208 ch /usr/share/ssl/misc
meillo@165 209
meillo@165 210 create new CA:
meillo@165 211 \begin{verbatim}
meillo@165 212 CA.pl -newca
meillo@165 213 country: DE
meillo@165 214 state: schwaben
meillo@165 215 city: Ulm
meillo@166 216 company:
meillo@165 217 section:
meillo@165 218 name:
meillo@165 219 emailaddress:
meillo@165 220 \end{verbatim}
meillo@165 221
meillo@165 222 generate ssl key:
meillo@165 223 \begin{verbatim}
meillo@165 224 CA.pl -newreq
meillo@165 225 ... the same questions
meillo@165 226 \end{verbatim}
meillo@165 227
meillo@165 228 sign request with CA:
meillo@165 229 \begin{verbatim}
meillo@165 230 CA.pl -sign
meillo@165 231 \end{verbatim}
meillo@165 232
meillo@165 233 remove passphrase from private key:
meillo@165 234 \begin{verbatim}
meillo@165 235 openssl rsa <newreq.pem >key.pem
meillo@165 236 (to be used by programs automaticly)
meillo@165 237 \end{verbatim}
meillo@165 238
meillo@165 239 secure:
meillo@165 240 \begin{verbatim}
meillo@165 241 chmod 400 *.pem
meillo@165 242 cp newcert.pem /etc/postfix/cert.pem
meillo@165 243 cp key.pem /etc/postfix/key.pem
meillo@165 244 cp demoCA/cacert.pem /etc/postfix/CAcert.pem
meillo@165 245 chmode 400 /etc/postfix/*.pem
meillo@165 246
meillo@165 247 mkdir /etc/stunnel
meillo@165 248 cat newcert.pem key.pem >/etc/stunnel/stunnel.pem
meillo@165 249 chmod 400 /etc/stunnel/stunnel.pem
meillo@165 250 (check /etc/stunnel with `stunnel -V')
meillo@165 251 \end{verbatim}
meillo@165 252
meillo@165 253
meillo@165 254 set up stunnels for POP, etc:
meillo@165 255 \begin{verbatim}
meillo@165 256 nmap localhost
meillo@165 257 stunnel -d pop3s -r localhost:pop3 -p /etc/stunnel/stunnel.pem
meillo@165 258 stunnel -d imaps -r localhost:imap -p /etc/stunnel/stunnel.pem
meillo@165 259 nmap localhost
meillo@165 260 pop3s 995
meillo@165 261 imaps 993
meillo@165 262 \end{verbatim}
meillo@165 263
meillo@165 264 do not use stunnel wit SMTP:
meillo@165 265 because all incoming mail would be from 127.0.0.1 !!
meillo@165 266 use STARTTLS instead
meillo@165 267
meillo@165 268 postfix: main.cf
meillo@165 269 \begin{verbatim}
meillo@165 270 smtpd_use_tls = yes
meillo@165 271 smtpd_tls_received_header = no (does not log in received headers)
meillo@165 272
meillo@165 273 smtpd_tls_key_file = /etc/postfix/key.pem
meillo@165 274 smtpd_tls_cert_file = /etc/postfix/cert.pem
meillo@165 275 smtpd_tls_CA_file = /etc/postfix/CAcert.pem
meillo@165 276
meillo@165 277 smtp_use_tls = yes (use TLS for sending)
meillo@165 278 smtp_tls_key_file = /etc/postfix/key.pem
meillo@165 279 smtp_tls_cert_file = /etc/postfix/cert.pem
meillo@165 280 smtp_tls_CA_file = /etc/postfix/CAcert.pem
meillo@165 281 \end{verbatim}
meillo@165 282
meillo@165 283
meillo@165 284
meillo@163 285
meillo@163 286 \subsubsection*{Spam prevention}
meillo@163 287
meillo@163 288
meillo@163 289 where to filter what
meillo@163 290
meillo@163 291
meillo@165 292 postfix:
meillo@165 293 content-filter: arbitrary programs that talk smtp, can filter, rewrite or delete mail
meillo@165 294 - before-queue-c-f: need to be fast, can prevent system load
meillo@165 295 - after-queue-c-f: need more resources in global, more load
meillo@165 296
meillo@165 297 exim:
meillo@165 298 acls: to filter, what to accept (hook into smtp dialog) (complex)
meillo@165 299 routers: take recipient address and choose a matching transport
meillo@165 300 transports: ways to deliver mail (smtp, local)
meillo@165 301
meillo@165 302
meillo@163 303 postfix: after-queue-content-filter (smtp communication)
meillo@165 304 exim: content-scan-feature (analyses the content: MIME stuff, blacklisted words, virus scanning) (all within smtp dialog)
meillo@163 305 sendmail: milter (tcp or unix sockets)
meillo@163 306
meillo@163 307 checks while smtp dialog (pre-queue): in MTA implemented (need to be fast)
meillo@163 308 checks when mail is accepted and queued: external (amavis, spamassassin)
meillo@163 309
meillo@163 310
meillo@163 311
meillo@165 312
meillo@165 313
meillo@165 314
meillo@165 315 what do do with recognized mail?
meillo@165 316 - reject (only possible if recognized during SMTP dialog)
meillo@165 317 - forward with added header line or changed subject
meillo@165 318 (eisentraut05: page 18--20)
meillo@165 319
meillo@165 320 check incoming and outgoing mail
meillo@165 321 (eisentraut05: page 21)
meillo@165 322
meillo@165 323
meillo@165 324 milter:
meillo@165 325 communication with external daemons via a special protocol
meillo@165 326 at various times in the smtp dialog possible
meillo@165 327 can reject, delete or alter messages
meillo@165 328 http://milter.org
meillo@165 329 (eisentraut05: page 69)
meillo@165 330
meillo@165 331
meillo@165 332 use SA with exim:
meillo@165 333 - with transport: piped into sa
meillo@165 334 - content-scanning-feature: with ACL during smtp dialog
meillo@165 335 - plugin: sa-exim
meillo@165 336 - within amavis
meillo@165 337
meillo@165 338 use SA with sendmail:
meillo@165 339 - with milter
meillo@165 340 - within mimedefang or amavis
meillo@165 341
meillo@165 342 use SA with postfix:
meillo@165 343 - within amavis or mailfilter
meillo@165 344
meillo@165 345
meillo@165 346 (eisentraut05: page 25) ``Ganz ohne Analyse während der SMTP-Phase kommt sowieso kein MTA aus, und es ist eine Frage der Einschätzung, wie weit man diese Phase belasten möchte.''
meillo@165 347
meillo@165 348
meillo@165 349 DNSBL can contain:
meillo@165 350 - open relays
meillo@165 351 - dynamic IP addresses
meillo@165 352 - verified spam sources
meillo@165 353 - open multistage relays
meillo@165 354 - vulnerable CGI scripts
meillo@165 355 - open proxy servers
meillo@165 356 example: NJABL (http://njabl.org)
meillo@165 357
meillo@165 358 DNSBL in smpt dialog is aggressive and can lead to problems (eisentraut05: page 126)
meillo@165 359
meillo@165 360
meillo@165 361 greylisting:
meillo@165 362 if first contact from that address: temp failure and add to list
meillo@165 363 sender will retry, then accept
meillo@165 364
meillo@165 365 ``Das Greylisting zählt derzeit zu den effektivsten Methoden, um gegen unerwünschte E-Mails vorzugehen. Allein durch Greylisting können derzeit rund 70\% des potenziellen Spam-Aufkommens auf einem Mailserver vollständig geblockt werden. Allerdings ist es auch nur eine Frage der Zeit, bis sich die Gemeinde der Spammer und Virenautoren auf diese Methode der Spam-Bekämpfung eingerichtet und entsprechende Queues in ihre Software eingebaut hat.''(eisentraut05: page 138)
meillo@165 366 Probleme: load balancing using multiple servers with different IPs.
meillo@165 367 postfix: with policy server
meillo@165 368 exim: direct in config
meillo@165 369 sendmail: with greylist milter
meillo@165 370
meillo@165 371
meillo@165 372
meillo@165 373 hashcash
meillo@163 374
meillo@163 375
meillo@163 376 \subsubsection*{Virus checking}
meillo@163 377
meillo@163 378 The same for malicious content (\name{malware}) like viruses, worms, trojan horses. They are related to spam, but affect the \MTA less, as they are in the mail body.
meillo@163 379
meillo@163 380 message body <-> envelope, header
meillo@163 381
meillo@163 382
meillo@163 383 anti-virus: clamav
meillo@165 384 postfix: via amavis
meillo@165 385 exim: via content-scanning-feature called from acl
meillo@165 386 sendmail: with milter
meillo@165 387 procmail
meillo@163 388
meillo@163 389
meillo@165 390 virus scanner work on file level
meillo@165 391 amavis receives mail via smtp or pipe, splits it in its parts (MIME) and extracks archives, the come the virus scanners
meillo@165 392 if the mail is okay, it goes via smtp to a second mta
meillo@165 393
meillo@165 394
meillo@165 395 AMaViS (amavisd-new): email filter framework to integrate spam and virus scanner
meillo@165 396 \begin{verbatim}
meillo@165 397 internet -->25 MTA -->10024 amavis -->10025 MTA --> reciptient
meillo@165 398 | |
meillo@165 399 +----------------------------+
meillo@165 400 \end{verbatim}
meillo@165 401
meillo@165 402 postfix and exim can habe both mta servises in the same instance, sendmail needs two instances running.
meillo@165 403
meillo@165 404 what amavis recognizes:
meillo@165 405 - invalid headers
meillo@165 406 - banned files
meillo@165 407 - viruses
meillo@165 408 - spam (using spam assassin)
meillo@165 409
meillo@165 410
meillo@165 411 mimedefang: uses milter interface with sendmail
meillo@165 412
meillo@165 413
meillo@165 414 MailScanner:
meillo@165 415 incoming queue --> MailScanner --> outgoing queue
meillo@165 416
meillo@165 417 postfix: with one instance possible, exim and sendmail need two instances running
meillo@165 418
meillo@163 419
meillo@163 420
meillo@163 421
meillo@163 422 \subsubsection*{Archiving}
meillo@163 423
meillo@163 424
meillo@165 425 \texttt{always\_bcc} feature of postfix
meillo@163 426
meillo@163 427
meillo@163 428
meillo@163 429 \section{A new architecture}
meillo@161 430
meillo@161 431
meillo@161 432 (ssl)
meillo@161 433 -> msg-in (local or remote protocol handlers)
meillo@161 434 -> spam-filter (and more)
meillo@161 435 -> queue
meillo@161 436 -> msg-out (local-delivery by MDA, or remote-protocol-handlers)
meillo@161 437 (ssl)
meillo@161 438
meillo@161 439
meillo@161 440
meillo@161 441
meillo@161 442
meillo@161 443 http://fanf.livejournal.com/50917.html %how not to design an mta - the sendmail command
meillo@161 444 http://fanf.livejournal.com/51349.html %how not to design an mta - partitioning for security
meillo@161 445 http://fanf.livejournal.com/61132.html %how not to design an mta - local delivery
meillo@161 446 http://fanf.livejournal.com/64941.html %how not to design an mta - spool file format
meillo@161 447 http://fanf.livejournal.com/65203.html %how not to design an mta - spool file logistics
meillo@161 448 http://fanf.livejournal.com/65911.html %how not to design an mta - more about log-structured MTA queues
meillo@161 449 http://fanf.livejournal.com/67297.html %how not to design an mta - more log-structured MTA queues
meillo@161 450 http://fanf.livejournal.com/70432.html %how not to design an mta - address verification
meillo@161 451 http://fanf.livejournal.com/72258.html %how not to design an mta - content scanning
meillo@161 452
meillo@161 453
meillo@161 454
meillo@132 455
meillo@132 456
meillo@137 457
meillo@137 458
meillo@149 459
meillo@149 460
meillo@149 461
meillo@149 462
meillo@149 463
meillo@149 464
meillo@149 465
meillo@149 466
meillo@93 467
meillo@93 468
meillo@99 469
meillo@93 470
meillo@93 471
meillo@161 472 \section{Directions to go}
meillo@161 473
meillo@161 474 This section discusses about what shapes \masqmail\ could have---which directions the development could go to.
meillo@161 475
meillo@93 476
meillo@146 477
meillo@146 478
meillo@146 479
meillo@146 480 \subsubsection*{\masqmail\ in five years}
meillo@146 481
meillo@146 482 Now how could \masqmail\ be like in, say, five years?
meillo@146 483
meillo@163 484 ---
meillo@163 485
meillo@163 486 A design from scratch?
meillo@163 487 << what would be needed (effort) >>
meillo@163 488 But how is the effort of this complete rewrite compared to what is gained afterwards?
meillo@163 489
meillo@163 490 << would one create it at all? >>
meillo@163 491
meillo@163 492 ---
meillo@163 493
meillo@146 494 << plans to get masqmail more popular again (if that is the goal) >>
meillo@146 495
meillo@146 496 << More users >>
meillo@146 497
meillo@146 498
meillo@146 499
meillo@146 500
meillo@163 501
meillo@163 502
meillo@163 503
meillo@93 504 \section{Work to do}
meillo@93 505
meillo@146 506 << short term goals --- long term goals >>
meillo@146 507
meillo@163 508 do it like sendmail: first do the most needed stuff on the old design to make it still usable. Then design a new version from scratch, for the future.
meillo@163 509
meillo@140 510 << which parts to take out and do within the thesis >>
meillo@93 511
meillo@167 512