That is actually not true. I tested both Gordano's communicator and Lyris Listmanager and both are able to handle this requirement without a problem. I guess we found one of mailman's real weaknesses then.
To enable custom headers for each message at least partially destroys the intent of a mailing list - efficient delivery of messages. If each message is customized that way then you have to actually send one distinct message to every user instead of sending a single message with multiple RCPT-TO lines. Enabling this would serve to radically increase the server overhead that Mailman causes (back to the Smartlist olden days). Instead of injecting one message to hundreds of recipients, you would be injecting hundreds of unique messages.
This is hardly a weakness of mailman and instead a weird bit of behaviour on AOLs part.
IMHO of course.
Cheers
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