anubis | an SMTP message submission daemon | Mehr ...
GNU Anubis is an intermediate layer between a mail user agent (MUA) and a mail transport agent (MTA), receiving messages from the MUA, applying to them a set of predefined changes and finally inserting modified messages into an MTA routing network. The set of changes applied to a message is configurable on a system-wide and per-user basis. The built-in configuration language used for defining sets of changes allows for considerable flexibility and is easily extensible.