smtpfront(8)

NAME

smtpfront - SMTP Front Ends

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:

o Validates senders and recipients according to ``mailrules'' process: ing.
o 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.
o Handles RFC 2554 SMTP authentication. After authentication all: recipients not rejected by mail rules are allowed, and back-end validation is omitted.
o Automatically handles either bare NL or RFC 821/2821 compliant CR/NL: end-of-line conventions.
o Rejects messages that exceed $DATABYTES bytes in the body.
o 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).
o Counts the number of "Received:" and "Delivered-To:" headers, and: rejects the message if more than $MAXHOPS of either are seen (defaults to 100).
o All error responses are logged.
o Handles (ignores) RFC 1869 extended parameters on the ``RCPT TO:'': and ``MAIL FROM:'' commands.
o Initial greeting message is configureable by $SMTPGREETING.
o Rejects bounce messages (messages with an empty envelope sender) that: attempt to deliver to multiple recipients.
o Optionally adds a fixup "Received:" header for hosts that have dif: ferent 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.

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See also