I've been running my own mail server on AWS for about 3 years now. Postfix, Dovecot, and a Rails app I wrote for webmail. At first I had 0 deliverability but over time it's improved to near 100%. Just setting up SPF, DKIM, not being on a blacklist, and building up a reputation of good mail seems to have worked wonders. I've been wanting to move to DigitalOcean but I don't yet know if there will be a significant hit on my IP reputation.

Postfix occasionally drops a legitimate incoming email due to a misconfigured sender, usually from a domain that doesn't resolve to anything, but I just log those in case I miss something important.