This isn’t quite a website bug, but this seems to be the closest category for it.
Exploits – If you discover an exploit in the game, do not exploit it or publicize it, but instead notify us immediately at this new email address: exploits (at) arena (dot) net.
My emails bounce back with an error from Daemon Mailer whenever I attempt to mail exploits@arena.net.
Delivery to the following recipient failed permanently:
exploits@arena.net
Technical details of permanent failure: Google tried to deliver your message, but it was rejected by the recipient domain. We recommend contacting the other email provider for further information about the cause of this error. The error that the other server returned was: 550 550 Recipient address rejected: User unknown (state 16).