One of the challenges I ran into moving to Digital Ocean is they don't provide a full Wordpress ready stack, most notably no SMTP mailer.
They said you just have to install Postmail yourself, which I tried to but failed with so much I gave up and asked if there was another option.
They suggested a Wordpress module, notably WP SMTP. I have installed this and configured it to use a third party SMTP sending service, and I got it to work for me fine.
However users have been saying they get no registrations email for CBPN.io, so it appears not all the time. So can I ask:
1) Could you try and see if you get emails
2) Help fix including suggesting any other possible scenarios for how to achieve the mail, I'm not wedded to WP SMTP