@jdaviescoates I was going to say just that. I've been using Mailgun ever since I spun up my first Cloudron server. No issues. I rarely log in, but emails are being sent/received daily. The lack of activity must be the reason for the account closure.
@LoudLemur If you're on the free/pay-as-you-go plan, make sure to add a credit card on file. That could be a reason too.