I think that’s unfair. Following the first set of directions for setting up Configuration - Adapt your publication to suit your needs works reliably at places that don’t block your outbound email.
Digital Ocean is blocking your outbound SMTP ports (except maybe 2525). That’s definitely ‘intentional’, but it isn’t about driving you into managed hosting. It’s about preventing spam and protecting their reputation. That’s not the Ghost team’s fault.
I recommended that you search the forum (because I was on my phone when I responded to you previously) for directions for the API, since I expect that DO will probably block port 2525 at some point, too. The first hit links to the second hit, which is this one, and includes a configuration file sample for how to use the API: Make onboarding emails also work via API (not only SMTP) - #4 by vikaspotluri123 . For anyone who comes later and needs it, I’ve updated the link above with a complete configuration example.
This is an excellent reason to select managed hosting. Self-hosting requires the willingness to deal with configuration issues, including linux server administration, mailserver adminstration, integrations, firewalls, database management, etc. It isn’t for everyone!
And yes, if you’re going to send a daily newsletter to a bunch of users, Ghost Pro is actually cheaper than Mailgun for some numbers of members.