Try getting your mails from your self-hosted DO server into the inbox at Outlook, Gmail, Yahoo etc. The big mail providers have it all relatively sewn up - anything coming from the likes of a random VM provider like DO will end up in 'spam.'
In case of my own DO mailserver, Yahoo will put you into deferred state for a while eventually will see other emails are not similar enough and give you a chance to go into main mailbox. Unless you have nasty friends who mark each of your email as spam, Outlook Gmail and Yahoo will let it thru to their main mailbox. Also most of my friends are checking spam folder once a week or so, and then its enough for Yahoo to get you to reply to that email once, to consider it being 2-way conversation and all my future emails go to their main inbox without any issues, helping my IP get better reputation.
TLDR: most stories of personal mailserver being bad idea because big guys will put you in spam are grossly overstated, unless you plan to use your server to send large amount of emails that contain marketing stuff.