SYNOPSIS

smtpfront

DESCRIPTION

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:

• Validates senders and recipients according to ``mailrules'' processing.
• If $RELAYCLIENT is set, all recipient addresses not rejected by mail rules are allowed, and its contents are appended to each recipient address. Back-end validation is omitted.
• 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 821/2821 compliant CR/NL end-of-line conventions.
• Rejects messages that exceed $DATABYTES bytes in the body.
• 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).
• Counts the number of "Received:" and "Delivered-To:" headers, and rejects the message if more than $MAXHOPS of either are seen (defaults to 100).
• 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.
• Rejects bounce messages (messages with an empty envelope sender) that attempt to deliver to multiple recipients.
• Optionally adds a fixup "Received:" header for hosts that have different incoming and outgoing hostnames or IPs. Set $FIXUP_RECEIVED_HOST and $FIXUP_RECEIVED_IP if you want this header added.

BACK ENDS

smtpfront-echo

Uses the echo backend to simply echo back the sender and recipient parameters, and the size of the data to the client.

smtpfront-qmail

Uses the ``qmail validation features'' to validate addresses, and the ``qmail backend'' to deliver messages.

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.