I noticed that there seems to be something wrong with the ispConfig configuration for Mail-Transport/-Routes.

I'm hosting a customers Web (WWW-Only!) whereas the Mail hosting is done by their own Exchange-Server. The DNS-Record correctly points to their own MX. But my Server (PHP based Web) tries to deliver them to the origin of the Customers-Domain A-Record (=My Machine responsible for WWW-Hosting only!).

Then I tried to enter the Domain as SMTP-Mail Route and then entered the Customers-Domain in Mail -> Global-Filters -> Relay Recipients.

But I noticed that "Relay Recipients" doesn't seem to accept a Domain-name by testing this route. My Smtp rejects the E-Mail send by my own E-Mail Account hosted on the same machine.

I would expect it right if the Domain-Name matching the "Relay-Transport" in MySQL would match the Domain-TLD of the outgoing E-Mail. Testing the same Route-Setup with a full E-Mail Address under the "Relay Recipients" in ispConfig works fine and confirms the wrong behaviour.

I think this can be fixed by altering the MySQL-Query in the Postfix's "mysql-virtual-transport" Query.