Here is a quick hack - a diff against newsportal-0.35pl1 - that provides users with the ability to filter out certain eMail addresses from discussions they're reading. It is not properly localised, and all kill file entries are global. Threads are cut off whenever a posting by a killed author shows up. This is probably a rather extreme way of filtering, and I hope to see this idea fine-tuned by others who are more at home with NewsPortal than me.
(Note: The diff placed here on 2004-12-12 was missing a language definition file. Corrected as of 2004-12-13 9:28 CET.)
Changes from v1 to v2: Added a versioning marker at the beginning of the killfile cookie so that a later change in the killfile cookie format will not (necessarly) render old-style cookies unworkable.
Please notify me if there is a problem.