Two critical bugs crept into the just released version of KMail. One is related to POP filters and the other to spam filtering - both cause mail loss! They are fixed in CVS and patches are linked on the KDE 3.2 Info Page. The distributors have been asked to update their binary packages.
If you are using POP filters with KMail then, after upgrading to KDE 3.2, you have to reconfigure your POP filters because otherwise messages which are supposed to be downloaded later will be deleted from the POP server. Also due to this bug you must not use KMail 1.6 (from KDE 3.2) and an older version of
KMail in parallel because both versions will behave differently (one version might download your messages from the server while the other version might delete your messages from the server).
If you filter email in an IMAP folder trough spamc the message may lose its UID and consequently a delete job is sent to the kio_imap slave without a UID. The slave unfortunately interprets that as "expunge folder".