I got this working thanks to Jaydisc's comment elsewhere:
"All of this is doable by manipulating postfix underneatht the hood. I haven't seen what file Mountain Lion specifically creates when you turn on virtual hosting, but traditionally these kind of mappings are stored in /etc/postfix/virtual. You need to postmap the file after making changes and restart postfix.
Jonathan, mailman is seemingly no longer included in OS X Server whicih would ahve been perfect. That means you need to manually build your list in /etc/postfix/virtual or install a 3rd party solution as far as I'm aware. In /etc/postfix/virtual, you could so something like:
email@example.com firstname.lastname@example.org, email@example.com, firstname.lastname@example.org
Levin, you don't want to do a catch-all, but if you insist, assuming it's with a virtual domain, you'd put in
When done, run:
Do all of this as root or using the sudo command. If you don't know what I'm talking about, you probably shouldn't do it."
I edited /etc/postfix/virtual via the command line, like:
sudo nano /etc/postfix/virtual
And add the group and the users like in the example above.
I now do want to catch all email as it has become my lives work to report spam.
So I figured out an easier way to catch all email using simply the serveradmin command-line tool (this only takes email that would otherwise bounce):
sudo serveradmin settings mail:imap:lmtp_luser_relay_enabled = yes
sudo serveradmin settings mail:imap:lmtp_luser_relay = catchallusername
sudo postfix reload