Mail going through my list has a From: line that points back to the original poster. I want this line to contain the list address instead.

While it is possible to configure the RFC822 header lines Reply-To: and Sender: via the Reply-To= and Sender= list header keywords, From: is not configurable. This is because, per RFC822, it must contain the address of the originator of the message.

For moderated lists where it is not desirable for the moderator's default e-mail address to show up in the From: line, you can simply use a second POP account and another instance of your POP client to moderate the list.

In any case, due to compliance with RFC822, LISTSERV itself is not allowed to change the value of the From: field except in rare instances where the From: field can't be parsed, and then it says something like '"Undetermined origin c/o LISTSERV Postmaster at node_x" <owner-LISTSERV@node_x>' (but of course, this is not considered a "change" because the original From: line has become garbled or is non-existent).