I had a user complain they couldn't receive emails while the master server was down because of a hardware fault. I had a look in the logs on the slave server and found: Recipient address rejected: User unknown in virtual mailbox table The master server is up now and I've had a look around in myphpadmin and found the alias is in dbispconfig/mail_forwarding but not in dbispconfig2/mail_forwarding. I'm using mysql master to master replication and I checked this is all working and it is. Should the master to master replication keeps these in sync? Knowing there is an issue how best should I check there aren't other issue? Thanks, Justin.