SMTP Front Ends
Overview
The code for SMTP is divided internally into two sections:
front-end and back-end code. The front-end code handles the low-level
details of the protocol. The back-end code handles the validation and
delivery details in a protocol-independant fashion.
Features
The following features are common to all SMTP front-ends:
- Handles RFC 2554
SMTP authentication. After authentication all recipients not rejected
by mail rules are allowed, and back-end validation is omitted.
- Automatically handles either bare NL or RFC 821 / RFC 2821 compliant
CR/NL end-of-line conventions.
- Times out connections after $TIMEOUT seconds of inactivity
(defaults to 1200 seconds or 20 minutes), or $SESSION_TIMEOUT
seconds after the connection was established (defaults to 86400 seconds
or 24 hours).
- All error responses are logged.
- Handles (ignores) RFC 1869 extended
parameters on the RCPT TO: and MAIL FROM: commands.
- Initial greeting message is configureable by
$SMTPGREETING.
- Supports RFC
1870 SMTP Service Extension for Message Size Declaration.
- If $MAXNOTIMPL is set, clients are disconnected if they
send more than the specified number of commands that result in a
"500 Not implemented." error.
Back Ends
- smtpfront-echo
Uses standard handlers with the echo backend to
simply echo back the sender and recipient parameters, and the size of
the data to the client.
- smtpfront-qmail
Uses standard handlers with the qmail validation features to validate
addresses, and the qmail backend to
deliver messages, and is MSA compliant.
- smtpfront-reject
If $SMTPREJECT is set,
all SMTP commands are rejected with this message. If the message
starts with a "-", a permanent error number is used and the
leading "-" is stripped. If $SMTPREJECT is not set,
it execs its command line.