I had an email server working, then it stopped, I restored to a known good snapshot, and it still doesn’t work. I’ve been troubleshooting for many months, and I’ve gotten nowhere. I don’t see how this isn’t an issue with digitalocean. What can I do to see why this is happening?

Currently, I decided to basically start over. I still have that known good snapshot that doesn’t work for some reason, but I’ve tried every single tutorial I can find. Nothing is working. Currently, I can send, but not receive external email. I don’t know where to go next. What can digitalocean do to help figure out what changed?