I ran my own debian-exim for about a decade until I got tired of the care and feeding. opensmtpd does look suitably low-maintenance and I might pick it if I ever wanted to do this again, but it was released after I gave up being an email admin. I still have the mail domain, but having the same email address for sixteen years means ending up on a lot of spam lists.
You run your own server so you can easily set it up to accept any email matching some simple rules. This means you can give a different email address to every online service you use. If one of them starts getting spam, blackhole it.
I have been running my own email server this way for about 10 years and I have never needed any kind of antispam measure except a simple .procmailrc.
I ran my own debian-exim for about a decade until I got tired of the care and feeding. opensmtpd does look suitably low-maintenance and I might pick it if I ever wanted to do this again, but it was released after I gave up being an email admin. I still have the mail domain, but having the same email address for sixteen years means ending up on a lot of spam lists.