We have been using ISPConfig to host for over a year. Without any problems. This past month we moved from a T1 circuit (Time Warner) to a fiber connection (Charter) on a different carrier - which meant new IP's for the servers. Everything has gone well except that some of our users are now getting the infamous: Recipient address rejected: User unknown in local recipient table Return email message. The odd part is that the emails being returned appear to be within Charter's domain for connectivity. I have poured over numerous forums and played with the Postfix main.cf to no avail. Any help in pointing me to the possible culprit would be greatly appreciated.