I have been a long time KMail user and love this email client. It has most of the features that I care about, like Message Threading, Spam Filtering, Disconnected IMAP et cetera.
KMail has good integration with SPAM Handling softwares like spamassassin and bogofilter. The KMail wizard will autoconfigure spamassassin, bogofilter and others (as detected from your installation). The default settings were a little annoying because messages detected as SPAM were re- written with the SPAM Heading. The problem was when spamassassin mis-judged a genuine message as SPAM. Well, we could mark it as HAM, but the added heading never went off.
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