Spam is another reason most places don't bother with selfhosting email now. Big providers like GMail aggressively filter unknown servers so if you attempt to host your own and don't setup everything perfectly (or even if you do and you trigger their filter ban threshold) all your email will silently fail to deliver or be blackholed to the Spam folder for the largest email providers and you might never find out or have a way to get them to reconsider.
Something I faced at multiple companies before Google and MS took over was that malware would get on your mail server and start blasting out spam. And then you'd find yourself on a bunch of blacklists thinking they made a mistake but it's because your server was actually spamming.
