Turns out, installing Mastodon is no simple feat.
So I got Mastodon running .. after some heavy fuckery with nginx. Now it seems it doesn't send any emails ..
It seems the problem is at Mailgun's side. Emails are being accepted, but never delivered. Google tells me Mailgun sometimes is an asshole. I opened a ticker so let's see what's up.
@digitalbaboon did you checked actual logs and see what is going on?