I've thought about rolling my own email service, but I'm hesitant given the risk of it inadvertently nuking the rest of my network. There's a lot of work needed to keep the thing secure, and even if you do everything right there's a good chance you get SMTP traffic blocked because other services are worried about unknown accidentally hosting spammer networks.
Plus given my prior track record, there is a $1000% chance I screw up the DNS entries for any mail servers I set up.