Interesting. I was transferred a little over 2 weeks ago and email forwarding seemed to work fine. Sometime around this morning, it stopped working and senders are seeing the following error:
host mxa.mailgun.org[34.160.157.95] said: 550 5.7.1
Relaying denied (in reply to RCPT TO command)
I've reported this to support, but haven't heard back yet. Looking at my DNS records, I see the same mailgun MX records as described by other posters