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It's possible to use SpamAssassin with every MUA (Mail User Agent) which supports some kind of "pipe through" filter.
Integrated in KMail
For current versions of KMail there's a description on the \[http://kmail.kde.org/tools.html#antispam KMail Tools\] page. The next version of KMail shipped with KDE-PIM 3.3 will have an antispam-wizard which makes building the filter rules a thing of three clicks. Wiki Markup