my server's ip address seems to be blocked, presumably because some previous DO user was spamming?
Yes, you have to then setup an Email relay in the
when I try to use my site's wordpress feed, I get an error:
Is this inside mailtrain? Where does that screenshot come from?
I noticed there is a mail plugin for wordpress already - do I even need mailtrain in that case? I was not able to get it to work because of (1) above though
You probably do not. Note that mailtrain is only required to send and manage newsletters (for example, to put unsubscribe links in your email etc). If you just want to send email, the wordpress app should work without requiring any configuration. I suspect it cannot send mail because of the problem in 1.
All certs are Let's Encrypt. The SSL issue appears to be something else but I am not 100% sure. Can you tell us a bit more high level of what you are trying to do and we can help out.