smtpd-pipe

A very minimal SMTP server that will only forward messages to shell commands via UNIX pipes. Its intended usage is to provide an SMTP endpoint for containerized services that expect to receive email over a pipe, without having to run a full MTA.

Usage

The daemon can be configured with a list of regular expression / shell command-line pairs: if a message matches a regular expression, the associated command will be executed. Messages that do not match anything will be rejected.

Rules (regexp / command pairs) are encoded as a colon-separated string pair (which implies that the regexp can't contain a colon). They can be passed to the program via the command-line option --rule (repeated multiple times), or via the environment variable SMTP_RULES, which should be a semicolon-separated list of rules.

Regular expressions are automatically anchored, so they should match the full recipient address, including the domain part (but there is no need to include the ^ and *

smtpd --rule='archive+(.*)@example.com:/usr/local/bin/archive $1'

Further command-line options are available to set network timeouts and various execution limits, see smtpd --help for details.