Quoting Jamie Zawinski <jwz@jwz.org>:
Say I have three smartlist lists on the same host. I send a single message to all three lists:
To: listA, listB, listC
If all three lists contain the same subscriber, that person gets three copies of the message. All three copies have the same (original) Message-ID, but different Resent-Message-IDs.
Is there any way to cause that person to only get one copy of the message instead of three?
SmartList can do nothing here without heavy modifications. It's rather a question of duplicate delivery suppression on the recipient or MTA site. E. g. the cyrus imap/pop3 server would deliver only one copy (with the default configuration). Probably there is also a solution at the MTA (postfix) side. You should ask the postfix community. Werner