I have a debian server set-up with sendmail and majordomo to handle incoming mail for some mailing-lists. Some of the users are in multiple lists and receive a mail twice when the mail is sent to both lists. Although not unexpected behavior it would be nice for these people to only receive the mail once.
So basically the question is: Is there a way to prevent sending a mail more then once to a recipient whom is in more then one (majordomo) list?
The strange thing is that I myself do not get the mail twice while using an internal user (as in part of the server) or when send to my student mail account. Somehow these servers filter out the duplicate mail.
A solution that could work for me is a way to rewrite the header when a message is send to email@example.com and firstname.lastname@example.org into email@example.com. Where firstname.lastname@example.org contains all members of list1 and list2 without duplicates.