meillo@75: from RFC821:
meillo@75: ------------
meillo@75: 
meillo@75: The following are the SMTP commands:
meillo@75: 
meillo@75: HELO <SP> <domain> <CRLF>
meillo@75: MAIL <SP> FROM:<reverse-path> <CRLF>
meillo@75: RCPT <SP> TO:<forward-path> <CRLF>
meillo@75: DATA <CRLF>
meillo@75: RSET <CRLF>
meillo@75: SEND <SP> FROM:<reverse-path> <CRLF>
meillo@75: SOML <SP> FROM:<reverse-path> <CRLF>
meillo@75: SAML <SP> FROM:<reverse-path> <CRLF>
meillo@75: VRFY <SP> <string> <CRLF>
meillo@75: EXPN <SP> <string> <CRLF>
meillo@75: HELP [<SP> <string>] <CRLF>
meillo@75: NOOP <CRLF>
meillo@75: QUIT <CRLF>
meillo@75: TURN <CRLF>
meillo@75: 
meillo@75: 
meillo@75: 4.2.2.  NUMERIC ORDER LIST OF REPLY CODES
meillo@75: 
meillo@75: 211 System status, or system help reply
meillo@75: 214 Help message
meillo@75: 	[Information on how to use the receiver or the meaning of a
meillo@75: 	particular non-standard command; this reply is useful only
meillo@75: 	to the human user]
meillo@75: 220 <domain> Service ready
meillo@75: 221 <domain> Service closing transmission channel
meillo@75: 250 Requested mail action okay, completed
meillo@75: 251 User not local; will forward to <forward-path>
meillo@75: 
meillo@75: 354 Start mail input; end with <CRLF>.<CRLF>
meillo@75: 
meillo@75: 421 <domain> Service not available,
meillo@75: 	 closing transmission channel
meillo@75: 	[This may be a reply to any command if the service knows it
meillo@75: 	must shut down]
meillo@75: 450 Requested mail action not taken: mailbox unavailable
meillo@75: 	[E.g., mailbox busy]
meillo@75: 451 Requested action aborted: local error in processing
meillo@75: 452 Requested action not taken: insufficient system storage
meillo@75: 
meillo@75: 500 Syntax error, command unrecognized
meillo@75: 	[This may include errors such as command line too long]
meillo@75: 501 Syntax error in parameters or arguments
meillo@75: 502 Command not implemented
meillo@75: 503 Bad sequence of commands
meillo@75: 504 Command parameter not implemented
meillo@75: 550 Requested action not taken: mailbox unavailable
meillo@75: 	[E.g., mailbox not found, no access]
meillo@75: 551 User not local; please try <forward-path>
meillo@75: 552 Requested mail action aborted: exceeded storage allocation
meillo@75: 553 Requested action not taken: mailbox name not allowed
meillo@75: 	[E.g., mailbox syntax incorrect]
meillo@75: 554 Transaction failed