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.'
Not necessarily true. A well configured mail server should be just fine. I personally use https://mailinabox.email/ to handle configuration for me and that works great.
If you're concerned about deliverability, you can also use a service like mail-tester.com [1], which receives a message you send and analyzes it for a wide variety of potential problems. I've found it to be a good guide.
that's only semi true, and probably true if you hadn't checked DO given IP address whether it was previously blacklisted in which case you need to create new server with hopefully pure IP.
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.