Version:           1.8 (using KDE 3.4.0, Gentoo)
Compiler:          gcc version 3.3.5 (Gentoo Linux 3.3.5-r1, ssp-3.3.2-3, pie-8.7.7.1)
OS:                Linux (i686) release 2.6.10-gentoo-r4

KMail 1.8-rc1 just suddenly crashed on me.  I have no clue what happened as it was in the background.

Maybe a minute before it crashed, I kicked off a folder expiry by setting the expire time of a folder which contained ~10000 mails from 186 days to 90 days (which cased ~5000 mails to be deleted).  It's possible that afterwards a message arrived in that folder.  I also started KAddressbook in between.

The last relevant debug statements from xsession-erros were:
kmail: (139008373, last 0) travel for SpamAssassin student developers? Daniel Quinlan, readyToShow true
kmail: parseMsg(KMMessage* aMsg == aMsg )
kmail: + Text/Plain
kmail:       Inserting one item into MimePartTree
kmail:                 Content-Type: Text/Plain
kmail: partNode::findType() is looking at Text/Plain
kmail: [static KMail::SpamScores KMail::SpamHeaderAnalyzer::getSpamScores(const KMMessage*)]
kabc: StdAddressBook::self()
kmail: ObjectTreeParser::parseObjectTree( node OK, showOnlyOneMimePart: FALSE )
kmail: KMReaderWin  -  finished parsing and displaying of message.
[...]
kwin: User timestamp, initial:10399387
kwin: User timestamp, ASN:10399387
kwin: User timestamp, final:'ID:8463084;WMCLASS:kmail:kmail;Caption:Mail Expiry Properties - KMail':10399387
kwin: Activation: Belongs to active application
[...]
kmail: ExpireJob: deleting unread older than 90 days
kmail: ExpireJob: deleting read older than 90 days
kmail: ExpireJob: starting to expire in folder /home/mss//.Mail/folders/.received.directory/.2: lists.directory/.SpamAssassin.directory/Talk
kmail: ExpireJob: finished expiring in folder /home/mss//.Mail/folders/.received.directory/.2: lists.directory/.SpamAssassin.directory/Talk 5323 messages t
o remove.
[...]
kmail: (139008357, last 0) RE: test Chris Santerre, readyToShow true
*** KMail got signal 11 (Crashing)
KCrash: crashing... crashRecursionCounter = 2
KCrash: Application Name = kmail path = <unknown> pid = 13645
DCOP: unregister 'kmail'
DCOP: register 'anonymous-16823' -> number of clients is now 21
DCOP:  'anonymous-16823' now known as 'drkonqi-16823'
kwin: User timestamp, initial:4294967295
kwin: User timestamp, ASN:4294967295
kwin: User timestamp, final:'ID:8388615;WMCLASS:drkonqi:drkonqi;Caption:KMail - The KDE Crash Handler':10552530
kwin: Activation, compared:'ID:8388615;WMCLASS:drkonqi:drkonqi;Caption:KMail - The KDE Crash Handler':10552530:10552905:false
kwin: Raising, compared:10503132:10559696:false
[...]
DCOP: unregister 'drkonqi-16823'
kwin: Raising, compared:10563559:10558256:true
kio_pop3: POP3Protocol::~POP3Protocol()
kdeinit: PID 16509 terminated.

The backtrace:
Using host libthread_db library "/lib/libthread_db.so.1".
[Thread debugging using libthread_db enabled]
[New Thread 16384 (LWP 13645)]
[KCrash handler]
#5  0x00000011 in ?? ()
#6  0x4046952b in KMMoveCommand::execute() ()
   from /usr/kde/3.4/lib/libkmailprivate.so
#7  0x4045fb47 in KMCommand::slotPostTransfer(KMCommand::Result) ()
   from /usr/kde/3.4/lib/libkmailprivate.so
#8  0x40454fb0 in KMCommand::qt_invoke(int, QUObject*) ()
   from /usr/kde/3.4/lib/libkmailprivate.so
#9  0x4045b79b in KMMenuCommand::qt_invoke(int, QUObject*) ()
   from /usr/kde/3.4/lib/libkmailprivate.so
#10 0x4045beda in KMMoveCommand::qt_invoke(int, QUObject*) ()
   from /usr/kde/3.4/lib/libkmailprivate.so
#11 0x429f85f2 in QObject::activate_signal(QConnectionList*, QUObject*) ()
   from /usr/qt/3/lib/libqt-mt.so.3
#12 0x40454d94 in KMCommand::messagesTransfered(KMCommand::Result) ()
   from /usr/kde/3.4/lib/libkmailprivate.so
#13 0x4045fb9d in KMCommand::transferSelectedMsgs() ()
   from /usr/kde/3.4/lib/libkmailprivate.so
#14 0x4045f993 in KMCommand::slotStart() ()
   from /usr/kde/3.4/lib/libkmailprivate.so
#15 0x40454f86 in KMCommand::qt_invoke(int, QUObject*) ()
   from /usr/kde/3.4/lib/libkmailprivate.so
#16 0x4045b79b in KMMenuCommand::qt_invoke(int, QUObject*) ()
   from /usr/kde/3.4/lib/libkmailprivate.so
#17 0x4045beda in KMMoveCommand::qt_invoke(int, QUObject*) ()
   from /usr/kde/3.4/lib/libkmailprivate.so
#18 0x429f85f2 in QObject::activate_signal(QConnectionList*, QUObject*) ()
   from /usr/qt/3/lib/libqt-mt.so.3
#19 0x42dd776a in QSignal::signal(QVariant const&) ()
   from /usr/qt/3/lib/libqt-mt.so.3
#20 0x42a18b0a in QSignal::activate() () from /usr/qt/3/lib/libqt-mt.so.3
#21 0x42a22b31 in QSingleShotTimer::event(QEvent*) ()
   from /usr/qt/3/lib/libqt-mt.so.3
#22 0x42988d7e in QApplication::internalNotify(QObject*, QEvent*) ()
   from /usr/qt/3/lib/libqt-mt.so.3
#23 0x42987ff5 in QApplication::notify(QObject*, QEvent*) ()
   from /usr/qt/3/lib/libqt-mt.so.3
#24 0x423b973b in KApplication::notify(QObject*, QEvent*) ()
   from /usr/kde/3.4/lib/libkdecore.so.4
#25 0x42974071 in QEventLoop::activateTimers() ()
   from /usr/qt/3/lib/libqt-mt.so.3
#26 0x429266d9 in QEventLoop::processEvents(unsigned) ()
   from /usr/qt/3/lib/libqt-mt.so.3
#27 0x4299f8a8 in QEventLoop::enterLoop() () from /usr/qt/3/lib/libqt-mt.so.3
#28 0x4299f6c4 in QEventLoop::exec() () from /usr/qt/3/lib/libqt-mt.so.3
#29 0x429890df in QApplication::exec() () from /usr/qt/3/lib/libqt-mt.so.3
#30 0x0804abbe in ?? ()
#31 0xbffff1b0 in ?? ()