Well, here are some ideas from an earlier threads:
List Software solution for email from OpenACS
https://openacs.org/bboard/q-and-a-fetch-msg.tcl?msg_id=0002rv
Email Autorespoder via AOLserver et.al.
https://openacs.org/bboard/q-and-a-fetch-msg.tcl?msg_id=0000mh
-Bob