Agent has pretty good filtering options, including regular expressions,
>but it will only filter on the From and Subject header lines.
>Using Hamster or another "local newsserver" like NFilter,
>exposes the other header lines
>so Path and Message-ID can be used by Hamster to score the message.
Note: The Gecko guys have promised the ability to filter on ANY header field in the next major release of Thunderbird (IceDove)/SeaMonkey (IceApe), due 1Q2008--so they recognize the need. (Hey, they still have 15 days to meet the schedule.)