Version:           unknown (using KDE 3.3.0, compiled sources)
Compiler:          gcc version 3.2.3
OS:                Linux (i686) release 2.6.7

Hard to say if that is helpful to reproduce or find the bug, ubt I was simply typing a reply message when suddenly kmail crashed with the following:
Using host libthread_db library "/lib/libthread_db.so.1".
[Thread debugging using libthread_db enabled]
[New Thread 16384 (LWP 29161)]
[KCrash handler]
#4  0x41a61abe in QShared::deref (this=0x38) at qshared.h:50
#5  0x41e1c962 in QString::deref (this=0x815a430) at tools/qstring.cpp:1548
#6  0x41e1ca18 in QString::operator= (this=0x815a430, s=@0xbfffdee0)
    at tools/qstring.cpp:1593
#7  0x40a85bc5 in KPIM::ProgressItem::setStatus (this=0x815a400, 
    v=@0xbfffdee0) at progressmanager.cpp:116
#8  0x40a986d9 in KPIM::BroadcastStatus::setStatusMsgTransmissionCompleted (
    this=0x8618980, numMessages=0, numBytes=-1073750352, numBytesRead=0, 
    numBytesToRead=36120, mLeaveOnServer=false, item=0x815a400)
    at broadcaststatus.cpp:99
#9  0x402d5331 in KMAcctExpPop::slotJobFinished (this=0x833bc60)
    at kmacctexppop.cpp:648
#10 0x402d40fb in KMAcctExpPop::slotCancel (this=0x833bc60)
    at kmacctexppop.cpp:233
#11 0x402da236 in KMAcctExpPop::slotResult (this=0x833bc60)
    at kmacctexppop.cpp:829
#12 0x402da796 in KMAcctExpPop::qt_invoke (this=0x833bc60, _id=9, 
    _o=0xbfffe360) at qucom_p.h:312
#13 0x41b2e32d in QObject::activate_signal (this=0x829a880, clist=0x8f1c0c0, 
    o=0xbfffe360) at kernel/qobject.cpp:2357
#14 0x41035527 in KIO::Job::result (this=0x829a880, t0=0x829a880)
    at jobclasses.moc:156
#15 0x4101c9f0 in KIO::Job::emitResult (this=0x829a880) at job.cpp:207
#16 0x4101e329 in KIO::SimpleJob::slotFinished (this=0x829a880) at job.cpp:524
#17 0x41021a71 in KIO::TransferJob::slotFinished (this=0x829a880)
    at job.cpp:884
#18 0x4101e62d in KIO::SimpleJob::slotError (this=0x829a880, error=56, 
    errorText=@0x9054a30) at job.cpp:535
#19 0x41035f31 in KIO::SimpleJob::qt_invoke (this=0x829a880, _id=151341616, 
    _o=0xbfffe730) at qucom_p.h:388
#20 0x4103730c in KIO::TransferJob::qt_invoke (this=0x829a880, _id=14, 
    _o=0xbfffe730) at jobclasses.moc:1061
#21 0x41b2e47a in QObject::activate_signal (this=0x81ed0c8, clist=0x8a9bee8, 
    o=0xbfffe730) at kernel/qobject.cpp:2381
#22 0x41010274 in KIO::SlaveInterface::error (this=0x81ed0c8, t0=28, 
    t1=@0xbfffe970) at slaveinterface.moc:214
#23 0x4100d3a5 in KIO::SlaveInterface::dispatch (this=0x81ed0c8, _cmd=102, 
    rawdata=@0xbfffe970) at slaveinterface.cpp:292
#24 0x4100c807 in KIO::SlaveInterface::dispatch (this=0x81ed0c8)
    at slaveinterface.cpp:191
#25 0x410096f4 in KIO::Slave::gotInput (this=0x81ed0c8) at slave.cpp:294
#26 0x4100bd49 in KIO::Slave::qt_invoke (this=0x81ed0c8, _id=4, _o=0xbfffeb50)
    at slave.moc:113
#27 0x41b2e32d in QObject::activate_signal (this=0x8f5b998, clist=0x842d390, 
    o=0xbfffeb50) at kernel/qobject.cpp:2357
#28 0x41b2e69f in QObject::activate_signal (this=0x8f5b998, signal=2, 
    param=15) at kernel/qobject.cpp:2450
#29 0x41e86c17 in QSocketNotifier::activated (this=0x8f5b998, t0=15)
    at .moc/debug-shared-mt/moc_qsocketnotifier.cpp:85
#30 0x41b4dfdc in QSocketNotifier::event (this=0x8f5b998, e=0xbfffedd0)
    at kernel/qsocketnotifier.cpp:280
#31 0x41acb65b in QApplication::internalNotify (this=0xbffff7b0, 
    receiver=0x8f5b998, e=0xbfffedd0) at kernel/qapplication.cpp:2635
#32 0x41acab18 in QApplication::notify (this=0xbffff7b0, receiver=0x8f5b998, 
    e=0xbfffedd0) at kernel/qapplication.cpp:2358
#33 0x41608ebf in KApplication::notify (this=0xbffff7b0, receiver=0x8f5b998, 
    event=0xbfffedd0) at kapplication.cpp:495
#34 0x41a60efb in QApplication::sendEvent (receiver=0x8f5b998, 
    event=0xbfffedd0) at qapplication.h:491
#35 0x41ab97f8 in QEventLoop::activateSocketNotifiers (this=0x80deba0)
    at kernel/qeventloop_unix.cpp:580
#36 0x41a72ee6 in QEventLoop::processEvents (this=0x80deba0, flags=4)
    at kernel/qeventloop_x11.cpp:383
#37 0x41adf94e in QEventLoop::enterLoop (this=0x80deba0)
    at kernel/qeventloop.cpp:198
#38 0x41acb849 in QApplication::enter_loop (this=0xbffff7b0)
    at kernel/qapplication.cpp:2790
#39 0x401efd41 in KMComposeWin::deadLetter (this=0x8e4e048)
    at kmcomposewin.cpp:648
#40 0x402e3e10 in KMKernel::dumpDeadLetters (this=0xbffff6d0)
    at kmkernel.cpp:1334
#41 0x402e6215 in KMKernel::qt_invoke (this=0xbffff6d0, _id=2, _o=0xbffff1e0)
    at kmkernel.moc:144
#42 0x41b2e32d in QObject::activate_signal (this=0x8326c88, clist=0x8326d40, 
    o=0xbffff1e0) at kernel/qobject.cpp:2357
#43 0x41b2e1cc in QObject::activate_signal (this=0x8326c88, signal=2)
    at kernel/qobject.cpp:2326
#44 0x41e87c78 in QTimer::timeout (this=0x8326c88)
    at .moc/debug-shared-mt/moc_qtimer.cpp:82
#45 0x41b52909 in QTimer::event (this=0x8326c88, e=0xbffff440)
    at kernel/qtimer.cpp:219
#46 0x41acb65b in QApplication::internalNotify (this=0xbffff7b0, 
    receiver=0x8326c88, e=0xbffff440) at kernel/qapplication.cpp:2635
#47 0x41acab18 in QApplication::notify (this=0xbffff7b0, receiver=0x8326c88, 
    e=0xbffff440) at kernel/qapplication.cpp:2358
#48 0x41608ebf in KApplication::notify (this=0xbffff7b0, receiver=0x8326c88, 
    event=0xbffff440) at kapplication.cpp:495
#49 0x41a60efb in QApplication::sendEvent (receiver=0x8326c88, 
    event=0xbffff440) at qapplication.h:491
#50 0x41ab96b0 in QEventLoop::activateTimers (this=0x80deba0)
    at kernel/qeventloop_unix.cpp:558
#51 0x41a72f05 in QEventLoop::processEvents (this=0x80deba0, flags=4)
    at kernel/qeventloop_x11.cpp:389
#52 0x41adf94e in QEventLoop::enterLoop (this=0x80deba0)
    at kernel/qeventloop.cpp:198
#53 0x41adf86a in QEventLoop::exec (this=0x80deba0)
    at kernel/qeventloop.cpp:145
#54 0x41acb7df in QApplication::exec (this=0xbffff7b0)
    at kernel/qapplication.cpp:2758
#55 0x0804a36c in main (argc=7, argv=0xbffff944) at kapplication.h:217