WHM installs Mailman by default. To disable Mailman on your server, perform one of following actions:
- Set the Enable Mailman mailing lists option in WHM's Tweak Settings interface (Home >> Server Configuration >> Tweak Settings) to No.
- Deselect the mailman option in the Enabled and Monitor columns of the Service Manager interface (Home >> Service Configuration >> Service Manager).
You can also disable it in your feature lists via "WHM Home » Packages » Feature Manager". It's normal to see "mailman" in the service manager, but it should remain disabled and show up without a check mark.