[clue] Self hosting email in 2015

[Yaverot]

How possible is this?  I've been trying to help a friend who needs to replace the Mac server he set up in 2003 or so. (And is well unsupported now, with no upgrade path).

Despite using multiple guides on the net, getting the software installed is a pain, the config files always seam to be somewhere else, and even after finally getting it setup, the server can only email to itself.  
Our most recent attempt was with iRedMail.

So the time has come to asking you enthusiasts on which expert to pay to get us setup and once again have a generally ignorable system that just works.

He's willing to try hosted email, as a temporary solution, pricing would be per domain not per user.  Actual volume of email I don't know at this time.  Local is required, the Denver-Boulder area.  

He needs to be able to add (or I assume remove) users/email addresses at will, with some type of GUI interface (web okay).
He wants to add an additional domain or two.
SSH access so that backup is an easy "ZFS send" command.  Which is a preference for FreeBSD over other options.  Although being set as a cron on the send side is preferred over a cron pull from the backup location. 
Webmail is unnecessary. IMAP is required.
Having the mail server within its own VM making moving it in the future easier, is a plus.

We already have a location with port 25 unblocked, that had been working fine for years until email providers started up-ing their security near the beginning of the year (and now quota limit warnings from a nearly-full drive).  He has control over the DNS records and can move the MX as needed.  

All the above, and I feel I'm missing something obvious.