[Mailman-Users] separate mailman and web servers

Can someone explain to me how mailman and the web server can exist on separate machines? I am new to mailman and I'm having a hard time understanding how mailman communicates with its web server. I have a new client that connects to an external web server to add list members but mailman (and postfix) runs on a local system.

I see that in /usr/local/mailman/Mailman/mm_cfg.py mailman is pointed to this external web server with DEFAULT_URL_HOST.

Any pointers on how postfix fits into this communication are also appreciated. The online docs at list.org for Site Administrators do not explain much.

What my client appears to have is a simple diffusion setup. They use it as a means to send info to multiple people. So members do not contribute.

P