The mail server crashed overnight with a hardware failure. They will not be repairing it, it will be restored to a new server. Looks like it has been down for 8-10 hours now and will likely be a few more. Here is the latest update from hosting...
UPDATE: We will be restoring this server to new hardware which will also mean an IP Address change. The restore is likely to take several hours however during this time mail that fails to deliver should bounce back to the sender. Whilst we will attempt to recover all mailboxes the backup is from a specific point in time so mail received in the past several hours may not be able to be recovered which we apologize for in advance.
The IP change mentioned will not affect you, you don't have to do anything. Any mail you sent to members overnight, subscription emails, and topic moved emails *may* be lost. We won't know until the move is done.