Mails should now work properly, also on my side since I was using the old Mailgun settings. I will have to use my personal address. Totally forgot about that 🤦
There is, however, still a chance that some mail will end up in the deferred mail queue. This is where invalid mails that couldn't be sent end up - such as when an E-Mail address is invalid or misspelt, FreeFlarum is not able to send it so it places it into this queue. So, if an E-Mail doesn't arrive at our server, there is a chance that it got caught there. In the case none of us replies within 24 hours, please re-send your mail.