Mac OS X Server: Multiple MTAs Cannot Share TCP Port 25

Symptom

When you start Apple Mail Service on port 25, you see an alert that says that the port is already in use by another application (such as sendmail).


Solution

1. Quit your current MTA so that it will release the port.
2. In Server Admin, click the Internet tab.
3. Choose Configure Mail Service from the Mail Service module.
4. Click the Protocols tab.
5. Choose SMTP from the "Use... for message transfer" pop-up menu.
6. Click Save.

Note: Be sure that your alternate MTA is not configured to restart automatically, such as when you restart the computer.