Specifically:
accept from any for domain lists.zx2c4.com virtual { "@lists.zx2c4.com" =>
mailman } deliver to mda "/var/lib/mailman/smtpd-deliver %{rcpt.user}"
Or in your case:
accept from any for domain opensmtpd.org virtual { "[email protected]" =>
mjllm } deliver to mda "/path/to/the/mjllmthing %{rcpt.user}"
The man page says:
"Mail is piped to the specified program, which is run with the privileges
of the user the message is destined to."
