There's been a *lot* of discussion about similar things wrt MLMs in general (qmail/ezmlm call this "VERP").

What it means is you must send N different messages, where N is the number of subscribers on your list, whereas now you send 1 message with M connections, where M is usually significantly less than M. So you drastically increase both filesystem and network load to do something like this.

Mailman doesn't currently support anything like this, although a custom Handlers/ module in 2.x will make it a lot easier to drop such a thing in, from what I can tell.

Before I start looking into this I thought I'd check to see if it's already been done/investigated.

I would like to include a line that says:

You are subscribed as: fife@AnwyhereYouGo.com

in the body of the message on the way out. I know it will increase the needed processing of messages tremendously, but it would be good for our subscribers as well as the list admin (me!). Our mail server doesn't have anything better to do anyway...