Used to run my own mail server 6 or 7 years ago, but stopped
At one point, it was getting 15k scans/hr from cracking scripts. Dealing with mail bombs, spam false positives, zero-day hacks etc. was making it a job to maintain.
IMHO, running your own mail server (and believing you are safer that way) is asking for headaches. There are so many more threats these days that it takes a team of people working 24/7 to keep highly vulnerable systems (like mail servers) safe. Never mind the spam and all the other things you should be doing on what is a production server (backups, system upgrades, etc).
Yes, you can probably run a mail server on your own, but other than a few select people who's day job involves doing this sort of thing at an industrial level, you are probably just going to create yet another easy to crack/abuse endpoint on the interwebs....
All my email is now hosted using Google Apps for Domains - I control the domain, Google deals with all the BS. Yes, they are scanning every inbound email, but they are also one of the only companies in the world to have successfully fended off nation-state sponsored hacking. Sure, they are close to TLAs, but to think that any one individual can realistically fend off a determined TLA focused on them is naive - at that point you are probably best off avoiding anything connected....
Biting the hand that feeds IT
