Most users install ListManager on a machine separate from their mail server. If necessary, they create a DNS Bypass in ListManager so ListManager sends mail properly to the mail server.
In most cases, you will spare yourself considerable work if you can find a machine that is not running a mail server, and install ListManager on that machine. Most mail server companies never planned on coexistence as a need and consequently made it impossible for ListManager to work with them.
The issue is that your mail server wants to receive all the mail sent to your machine, and thus ListManager never gets a chance to see its own mail.
There are three techniques for having ListManager coexist with your mail server on the same machine:
1. Assign Mail Server and ListManager Different IP Addresses
If your machine has more than one TCP/IP address and you can tell your mail server to leave at least one of those TCP/IP addresses unused, then ListManager can coexist on one (or multiple) TCP/IP addresses, and your mail server can exist on another.
You may set which IP addresses ListManager listens to in Utilities: Administration: Server: Server Settings: Machine Settings: IP Addresses.
2. Mail Server Forwards Mail to ListManager.
Configure ListManager to receive mail on a different port (port 26 is common) and then configure your mail server to forward mail on to ListManager running on a different port. To use this technique, you set up an alias for your machine (by adding a DNS 'A' RECORD) and inform your mail server that mail received for this address should be forwarded to ListManager that is running on a different port.
You may set which port ListManager listens to in Utilities: Administration: Server: Server Settings: Network Settings: Ports.
3. ListManager Forwards Mail to Mail Server
Configure your mail server to use another port, let ListManager answer mail on port 25, and inform it to forward non-ListManager mail on to your mail server that is running on an alternate port.
To instruct ListManager to forward non-ListManager mail, specify the IP address and port of your mail server in Utilities: Administration: Server: Server Settings: Network Settings: Receive Email.