What is Duplicate Delivery Supression / How does it work?

Duplicate delivery supression is a feature of the Cyrus IMAP server that allows multiple copies of an identical messages delivered to one user to be supressed, so that the user only recieves one copy. This can be conveinent if, say, one user is on multiple mailing lists that commonly recieve the same message.

The way that a message is determined to be a duplicate is a lookup is done in the duplicate delivery database for a message-id/mailbox pair. If a match is found, the message is supressed. If a match is not found, the pair is added to the database and the message is delivered.

Duplicate Delivery Supression can also affect sieve redirects. In this case, supression is done on a message-id/redirect-target basis.

Duplicate Delivery Supression can also affect vacation messages. In this case, supression is done based on a hash of the sender's address and the vacation message.

-- RobSiemborski? - 14 Aug 2003