I don't know off hand. 10.6 server had a mail server, but I never used it and don't remember what security it asks for.
I extremely recommend against this, however. You'll be opening your networks and machines up to bad misuse and there's a high possibility your resources will be misused by spammers and phishers. Plus, while a machine that does relay for another isn't strictly speaking unheard of, it's a very very uncommon setup.
So, I would recommend against thinking about running an email server unless you want, specifically, to be responsible for running an email server and all of the attendant work that goes along with it.
Hold on for vtools, contributors to the patreon will be able to get @vtools.68kmla.org email accounts that should be compatible with email programs.