mailinglist container

I was thinking of adding a temporary mailinglist for a few users, and was researching a bit mailman and mlmmj. I thought about putting it in a (stateless) container. But first thing I noticed was that they expect the MTA to deliver mails in some folder.
So I think I need something tiny that listens on a port and just transfers the message to the file.
Any ideas what I could use for dumping messages into a remote container?