Hi Michael! Thanks for the response. I miss you guys so much! 
Hmm.. I just moved my site from DO to Hetzner and it worked fine for a couple of weeks. My other site is working fine too. It’s a puzzle. Only sometime about a week ago it stopped working and when I looked into it saw the errors. I reached out to Hetzner (declined to help) and to Mailgun. According to Mailgun:
Thank you for your reply, the last accepted authenticated event we are seeing was on Jan 11th and was sent via SMTP.
Can you please confirm if any changes have been made? Please provide a screenshot of your sending application configuration for our review, as well as any relevant errors on your sending application/ SMTP sending logs.
I just changed my mailgun password in case that was it and tried again, but no dice.
rake emails:test output:
root@ubuntu-4gb-nbg1-1-app:/var/www/discourse# rake emails:test
Testing sending to using smtp.mailgun.org:587, username:postmaster@domain with plain auth.
====================================================================================== ERROR =======================================================================================
UNKNOWN ERROR!
EOFError: end of file reached
===================================================================================== SOLUTION =====================================================================================
This is not a common error. No recommended solution exists!
Please report the exact error message above to https://meta.discourse.org/
(And a solution, if you find one!)
====================================================================================================================================================================================