this crash still occures in 4.2.95/4.3rc1 from time to time.
in my case, i hit the send button and kmail/kontact crashed

here's the backtrace:
Application: Kontact (kontact), signal: Segmentation fault
[Current thread is 0 (LWP 16070)]

Thread 5 (Thread 0xab124b90 (LWP 16126)):
#0  0xb7f34430 in __kernel_vsyscall ()
#1  0xb509a0e5 in pthread_cond_wait@@GLIBC_2.3.2 () from /lib/tls/i686/cmov/libpthread.so.0
#2  0xb58ba2ed in __pthread_cond_wait (cond=0xa2afd78, mutex=0xa2afd60) at forward.c:139
#3  0xb5a9d5b2 in QWaitCondition::wait (this=0xa2afca8, mutex=0xa2378b8, time=4294967295) at thread/qwaitcondition_unix.cpp:87
#4  0xb0c2a148 in ThreadWeaver::WeaverImpl::blockThreadUntilJobsAreBeingAssigned (this=0xa2afc90, th=0x9f065a8) at /build/buildd/kde4libs-4.2.95/threadweaver/Weaver/WeaverImpl.cpp:365
#5  0xb0c2ceec in ThreadWeaver::WorkingHardState::waitForAvailableJob (this=0xa2058f0, th=0x9f065a8) at /build/buildd/kde4libs-4.2.95/threadweaver/Weaver/WorkingHardState.cpp:80
#6  0xb0c28d2b in ThreadWeaver::WeaverImpl::waitForAvailableJob (this=0xa2afc90, th=0x9f065a8) at /build/buildd/kde4libs-4.2.95/threadweaver/Weaver/WeaverImpl.cpp:356
#7  0xb0c2cfea in ThreadWeaver::WorkingHardState::applyForWork (this=0xa2058f0, th=0x9f065a8) at /build/buildd/kde4libs-4.2.95/threadweaver/Weaver/WorkingHardState.cpp:71
#8  0xb0c2a6d3 in ThreadWeaver::WeaverImpl::applyForWork (this=0xa2afc90, th=0x9f065a8, previous=0x0) at /build/buildd/kde4libs-4.2.95/threadweaver/Weaver/WeaverImpl.cpp:351
#9  0xb0c2d009 in ThreadWeaver::WorkingHardState::applyForWork (this=0xa2058f0, th=0x9f065a8) at /build/buildd/kde4libs-4.2.95/threadweaver/Weaver/WorkingHardState.cpp:74
#10 0xb0c2a6d3 in ThreadWeaver::WeaverImpl::applyForWork (this=0xa2afc90, th=0x9f065a8, previous=0x0) at /build/buildd/kde4libs-4.2.95/threadweaver/Weaver/WeaverImpl.cpp:351
#11 0xb0c2d009 in ThreadWeaver::WorkingHardState::applyForWork (this=0xa2058f0, th=0x9f065a8) at /build/buildd/kde4libs-4.2.95/threadweaver/Weaver/WorkingHardState.cpp:74
#12 0xb0c2a6d3 in ThreadWeaver::WeaverImpl::applyForWork (this=0xa2afc90, th=0x9f065a8, previous=0x0) at /build/buildd/kde4libs-4.2.95/threadweaver/Weaver/WeaverImpl.cpp:351
#13 0xb0c2d009 in ThreadWeaver::WorkingHardState::applyForWork (this=0xa2058f0, th=0x9f065a8) at /build/buildd/kde4libs-4.2.95/threadweaver/Weaver/WorkingHardState.cpp:74
#14 0xb0c2a6d3 in ThreadWeaver::WeaverImpl::applyForWork (this=0xa2afc90, th=0x9f065a8, previous=0xafea118) at /build/buildd/kde4libs-4.2.95/threadweaver/Weaver/WeaverImpl.cpp:351
#15 0xb0c2afbe in ThreadWeaver::ThreadRunHelper::run (this=0xab124330, parent=0xa2afc90, th=0x9f065a8) at /build/buildd/kde4libs-4.2.95/threadweaver/Weaver/Thread.cpp:87
#16 0xb0c2b5fb in ThreadWeaver::Thread::run (this=0x9f065a8) at /build/buildd/kde4libs-4.2.95/threadweaver/Weaver/Thread.cpp:142
#17 0xb5a9c56e in QThreadPrivate::start (arg=0x9f065a8) at thread/qthread_unix.cpp:189
#18 0xb50964ff in start_thread (arg=0xab124b90) at pthread_create.c:297
#19 0xb58ab49e in clone () at ../sysdeps/unix/sysv/linux/i386/clone.S:130

Thread 4 (Thread 0xaa923b90 (LWP 16129)):
#0  0xb7f34430 in __kernel_vsyscall ()
#1  0xb509a0e5 in pthread_cond_wait@@GLIBC_2.3.2 () from /lib/tls/i686/cmov/libpthread.so.0
#2  0xb58ba2ed in __pthread_cond_wait (cond=0xa2afd78, mutex=0xa2afd60) at forward.c:139
#3  0xb5a9d5b2 in QWaitCondition::wait (this=0xa2afca8, mutex=0xa2378b8, time=4294967295) at thread/qwaitcondition_unix.cpp:87
#4  0xb0c2a148 in ThreadWeaver::WeaverImpl::blockThreadUntilJobsAreBeingAssigned (this=0xa2afc90, th=0xa043050) at /build/buildd/kde4libs-4.2.95/threadweaver/Weaver/WeaverImpl.cpp:365
#5  0xb0c2ceec in ThreadWeaver::WorkingHardState::waitForAvailableJob (this=0xa2058f0, th=0xa043050) at /build/buildd/kde4libs-4.2.95/threadweaver/Weaver/WorkingHardState.cpp:80
#6  0xb0c28d2b in ThreadWeaver::WeaverImpl::waitForAvailableJob (this=0xa2afc90, th=0xa043050) at /build/buildd/kde4libs-4.2.95/threadweaver/Weaver/WeaverImpl.cpp:356
#7  0xb0c2cfea in ThreadWeaver::WorkingHardState::applyForWork (this=0xa2058f0, th=0xa043050) at /build/buildd/kde4libs-4.2.95/threadweaver/Weaver/WorkingHardState.cpp:71
#8  0xb0c2a6d3 in ThreadWeaver::WeaverImpl::applyForWork (this=0xa2afc90, th=0xa043050, previous=0x0) at /build/buildd/kde4libs-4.2.95/threadweaver/Weaver/WeaverImpl.cpp:351
#9  0xb0c2d009 in ThreadWeaver::WorkingHardState::applyForWork (this=0xa2058f0, th=0xa043050) at /build/buildd/kde4libs-4.2.95/threadweaver/Weaver/WorkingHardState.cpp:74
#10 0xb0c2a6d3 in ThreadWeaver::WeaverImpl::applyForWork (this=0xa2afc90, th=0xa043050, previous=0xb010998) at /build/buildd/kde4libs-4.2.95/threadweaver/Weaver/WeaverImpl.cpp:351
#11 0xb0c2afbe in ThreadWeaver::ThreadRunHelper::run (this=0xaa923330, parent=0xa2afc90, th=0xa043050) at /build/buildd/kde4libs-4.2.95/threadweaver/Weaver/Thread.cpp:87
#12 0xb0c2b5fb in ThreadWeaver::Thread::run (this=0xa043050) at /build/buildd/kde4libs-4.2.95/threadweaver/Weaver/Thread.cpp:142
#13 0xb5a9c56e in QThreadPrivate::start (arg=0xa043050) at thread/qthread_unix.cpp:189
#14 0xb50964ff in start_thread (arg=0xaa923b90) at pthread_create.c:297
#15 0xb58ab49e in clone () at ../sysdeps/unix/sysv/linux/i386/clone.S:130

Thread 3 (Thread 0xaa122b90 (LWP 16132)):
#0  0xb7f34430 in __kernel_vsyscall ()
#1  0xb509a0e5 in pthread_cond_wait@@GLIBC_2.3.2 () from /lib/tls/i686/cmov/libpthread.so.0
#2  0xb58ba2ed in __pthread_cond_wait (cond=0xa2afd78, mutex=0xa2afd60) at forward.c:139
#3  0xb5a9d5b2 in QWaitCondition::wait (this=0xa2afca8, mutex=0xa2378b8, time=4294967295) at thread/qwaitcondition_unix.cpp:87
#4  0xb0c2a148 in ThreadWeaver::WeaverImpl::blockThreadUntilJobsAreBeingAssigned (this=0xa2afc90, th=0xb035ff0) at /build/buildd/kde4libs-4.2.95/threadweaver/Weaver/WeaverImpl.cpp:365
#5  0xb0c2ceec in ThreadWeaver::WorkingHardState::waitForAvailableJob (this=0xa2058f0, th=0xb035ff0) at /build/buildd/kde4libs-4.2.95/threadweaver/Weaver/WorkingHardState.cpp:80
#6  0xb0c28d2b in ThreadWeaver::WeaverImpl::waitForAvailableJob (this=0xa2afc90, th=0xb035ff0) at /build/buildd/kde4libs-4.2.95/threadweaver/Weaver/WeaverImpl.cpp:356
#7  0xb0c2cfea in ThreadWeaver::WorkingHardState::applyForWork (this=0xa2058f0, th=0xb035ff0) at /build/buildd/kde4libs-4.2.95/threadweaver/Weaver/WorkingHardState.cpp:71
#8  0xb0c2a6d3 in ThreadWeaver::WeaverImpl::applyForWork (this=0xa2afc90, th=0xb035ff0, previous=0xaf77ed0) at /build/buildd/kde4libs-4.2.95/threadweaver/Weaver/WeaverImpl.cpp:351
#9  0xb0c2afbe in ThreadWeaver::ThreadRunHelper::run (this=0xaa122330, parent=0xa2afc90, th=0xb035ff0) at /build/buildd/kde4libs-4.2.95/threadweaver/Weaver/Thread.cpp:87
#10 0xb0c2b5fb in ThreadWeaver::Thread::run (this=0xb035ff0) at /build/buildd/kde4libs-4.2.95/threadweaver/Weaver/Thread.cpp:142
#11 0xb5a9c56e in QThreadPrivate::start (arg=0xb035ff0) at thread/qthread_unix.cpp:189
#12 0xb50964ff in start_thread (arg=0xaa122b90) at pthread_create.c:297
#13 0xb58ab49e in clone () at ../sysdeps/unix/sysv/linux/i386/clone.S:130

Thread 2 (Thread 0xa9826b90 (LWP 16135)):
#0  0xb7f34430 in __kernel_vsyscall ()
#1  0xb509a0e5 in pthread_cond_wait@@GLIBC_2.3.2 () from /lib/tls/i686/cmov/libpthread.so.0
#2  0xb58ba2ed in __pthread_cond_wait (cond=0xa2afd78, mutex=0xa2afd60) at forward.c:139
#3  0xb5a9d5b2 in QWaitCondition::wait (this=0xa2afca8, mutex=0xa2378b8, time=4294967295) at thread/qwaitcondition_unix.cpp:87
#4  0xb0c2a148 in ThreadWeaver::WeaverImpl::blockThreadUntilJobsAreBeingAssigned (this=0xa2afc90, th=0xacdc9e8) at /build/buildd/kde4libs-4.2.95/threadweaver/Weaver/WeaverImpl.cpp:365
#5  0xb0c2ceec in ThreadWeaver::WorkingHardState::waitForAvailableJob (this=0xa2058f0, th=0xacdc9e8) at /build/buildd/kde4libs-4.2.95/threadweaver/Weaver/WorkingHardState.cpp:80
#6  0xb0c28d2b in ThreadWeaver::WeaverImpl::waitForAvailableJob (this=0xa2afc90, th=0xacdc9e8) at /build/buildd/kde4libs-4.2.95/threadweaver/Weaver/WeaverImpl.cpp:356
#7  0xb0c2cfea in ThreadWeaver::WorkingHardState::applyForWork (this=0xa2058f0, th=0xacdc9e8) at /build/buildd/kde4libs-4.2.95/threadweaver/Weaver/WorkingHardState.cpp:71
#8  0xb0c2a6d3 in ThreadWeaver::WeaverImpl::applyForWork (this=0xa2afc90, th=0xacdc9e8, previous=0x0) at /build/buildd/kde4libs-4.2.95/threadweaver/Weaver/WeaverImpl.cpp:351
#9  0xb0c2d009 in ThreadWeaver::WorkingHardState::applyForWork (this=0xa2058f0, th=0xacdc9e8) at /build/buildd/kde4libs-4.2.95/threadweaver/Weaver/WorkingHardState.cpp:74
#10 0xb0c2a6d3 in ThreadWeaver::WeaverImpl::applyForWork (this=0xa2afc90, th=0xacdc9e8, previous=0x0) at /build/buildd/kde4libs-4.2.95/threadweaver/Weaver/WeaverImpl.cpp:351
#11 0xb0c2afbe in ThreadWeaver::ThreadRunHelper::run (this=0xa9826330, parent=0xa2afc90, th=0xacdc9e8) at /build/buildd/kde4libs-4.2.95/threadweaver/Weaver/Thread.cpp:87
#12 0xb0c2b5fb in ThreadWeaver::Thread::run (this=0xacdc9e8) at /build/buildd/kde4libs-4.2.95/threadweaver/Weaver/Thread.cpp:142
#13 0xb5a9c56e in QThreadPrivate::start (arg=0xacdc9e8) at thread/qthread_unix.cpp:189
#14 0xb50964ff in start_thread (arg=0xa9826b90) at pthread_create.c:297
#15 0xb58ab49e in clone () at ../sysdeps/unix/sysv/linux/i386/clone.S:130

Thread 1 (Thread 0xb47aeb30 (LWP 16070)):
[KCrash Handler]
#6  0xb5ba7701 in QMetaObject::activate (sender=0xb262378, m=0xb77b1bc8, local_signal_index=1, argv=0xbf94e7c8) at kernel/qobject.cpp:3190
#7  0xb773e029 in KPIM::ProgressItem::progressItemProgress (this=0xb262378, _t1=0xb262378, _t2=0) at /build/buildd/kdepim-4.2.95a/obj-i486-linux-gnu/libkdepim/progressmanager.moc:104
#8  0xb773e05b in KPIM::ProgressItem::setProgress (this=0xb262378, v=0) at /build/buildd/kdepim-4.2.95a/libkdepim/progressmanager.cpp:107
#9  0xb0e7dfc4 in KMAcctImap::postProcessNewMail (this=0x9f94a60, folder=0xa25f510) at /build/buildd/kdepim-4.2.95a/libkdepim/progressmanager.h:141
#10 0xb0e7f0a7 in KMAcctImap::qt_metacall (this=0x9f94a60, _c=QMetaObject::InvokeMetaMethod, _id=3, _a=0xbf94ea1c) at /build/buildd/kdepim-4.2.95a/obj-i486-linux-gnu/kmail/kmacctimap.moc:85
#11 0xb5ba6a58 in QMetaObject::activate (sender=0xa276768, from_signal_index=23, to_signal_index=23, argv=0xbf94ea1c) at kernel/qobject.cpp:3120
#12 0xb5ba76e2 in QMetaObject::activate (sender=0xa276768, m=0xb13be368, local_signal_index=19, argv=0xbf94ea1c) at kernel/qobject.cpp:3194
#13 0xb0de17d3 in FolderStorage::numUnreadMsgsChanged (this=0xa276768, _t1=0xa25f510) at /build/buildd/kdepim-4.2.95a/obj-i486-linux-gnu/kmail/folderstorage.moc:288
#14 0xb0e90dbb in KMFolderImap::slotCompleteMailCheckProgress (this=0xa276768) at /build/buildd/kdepim-4.2.95a/kmail/kmfolderimap.cpp:2337
#15 0xb0e98032 in KMFolderImap::slotStatResult (this=0xa276768, job=0xbf19d28) at /build/buildd/kdepim-4.2.95a/kmail/kmfolderimap.cpp:2200
#16 0xb0ea6ef6 in KMFolderImap::qt_metacall (this=0xa276768, _c=QMetaObject::InvokeMetaMethod, _id=35, _a=0xbf94ebfc) at /build/buildd/kdepim-4.2.95a/obj-i486-linux-gnu/kmail/kmfolderimap.moc:190
#17 0xb5ba6a58 in QMetaObject::activate (sender=0xbf19d28, from_signal_index=7, to_signal_index=7, argv=0xbf94ebfc) at kernel/qobject.cpp:3120
#18 0xb5ba76e2 in QMetaObject::activate (sender=0xbf19d28, m=0xb5f25da8, local_signal_index=3, argv=0xbf94ebfc) at kernel/qobject.cpp:3194
#19 0xb5dcbc23 in KJob::result (this=0xbf19d28, _t1=0xbf19d28) at /build/buildd/kde4libs-4.2.95/obj-i486-linux-gnu/kdecore/kjob.moc:188
#20 0xb5dcc0c9 in KJob::emitResult (this=0xbf19d28) at /build/buildd/kde4libs-4.2.95/kdecore/jobs/kjob.cpp:304
#21 0xb6eef5a5 in KIO::SimpleJob::slotFinished (this=0xbf19d28) at /build/buildd/kde4libs-4.2.95/kio/kio/job.cpp:477
#22 0xb6eef6da in KIO::StatJob::slotFinished (this=0xbf19d28) at /build/buildd/kde4libs-4.2.95/kio/kio/job.cpp:823
#23 0xb6eed12b in KIO::StatJob::qt_metacall (this=0xbf19d28, _c=QMetaObject::InvokeMetaMethod, _id=2, _a=0xbf94edc8) at /build/buildd/kde4libs-4.2.95/obj-i486-linux-gnu/kio/jobclasses.moc:234
#24 0xb5ba6a58 in QMetaObject::activate (sender=0xa1f40f0, from_signal_index=8, to_signal_index=8, argv=0x0) at kernel/qobject.cpp:3120
#25 0xb5ba76e2 in QMetaObject::activate (sender=0xa1f40f0, m=0xb7097f44, local_signal_index=4, argv=0x0) at kernel/qobject.cpp:3194
#26 0xb6fb5497 in KIO::SlaveInterface::finished (this=0xa1f40f0) at /build/buildd/kde4libs-4.2.95/obj-i486-linux-gnu/kio/slaveinterface.moc:165
#27 0xb6fb91d7 in KIO::SlaveInterface::dispatch (this=0xa1f40f0, _cmd=104, rawdata=@0xbf94ef94) at /build/buildd/kde4libs-4.2.95/kio/kio/slaveinterface.cpp:175
#28 0xb6fb5977 in KIO::SlaveInterface::dispatch (this=0xa1f40f0) at /build/buildd/kde4libs-4.2.95/kio/kio/slaveinterface.cpp:91
#29 0xb6fa76ed in KIO::Slave::gotInput (this=0xa1f40f0) at /build/buildd/kde4libs-4.2.95/kio/kio/slave.cpp:322
#30 0xb6fa9b83 in KIO::Slave::qt_metacall (this=0xa1f40f0, _c=QMetaObject::InvokeMetaMethod, _id=2, _a=0xbf94f0a8) at /build/buildd/kde4libs-4.2.95/obj-i486-linux-gnu/kio/slave.moc:76
#31 0xb5ba6a58 in QMetaObject::activate (sender=0xba52ea8, from_signal_index=4, to_signal_index=4, argv=0x0) at kernel/qobject.cpp:3120
#32 0xb5ba76e2 in QMetaObject::activate (sender=0xba52ea8, m=0xb7094880, local_signal_index=0, argv=0x0) at kernel/qobject.cpp:3194
#33 0xb6eb4147 in KIO::Connection::readyRead (this=0xba52ea8) at /build/buildd/kde4libs-4.2.95/obj-i486-linux-gnu/kio/connection.moc:86
#34 0xb6eb5ab3 in KIO::ConnectionPrivate::dequeue (this=0xbf44f78) at /build/buildd/kde4libs-4.2.95/kio/kio/connection.cpp:82
#35 0xb6eb5e96 in KIO::Connection::qt_metacall (this=0xba52ea8, _c=QMetaObject::InvokeMetaMethod, _id=1, _a=0xbf3f800) at /build/buildd/kde4libs-4.2.95/obj-i486-linux-gnu/kio/connection.moc:73
#36 0xb5b9f6ab in QMetaCallEvent::placeMetaCall (this=0xc4aed98, object=0xba52ea8) at kernel/qobject.cpp:489
#37 0xb5ba1150 in QObject::event (this=0xba52ea8, e=0xc4aed98) at kernel/qobject.cpp:1118
#38 0xb604ebcc in QApplicationPrivate::notify_helper (this=0x9cf8470, receiver=0xba52ea8, e=0xc4aed98) at kernel/qapplication.cpp:4057
#39 0xb6056ede in QApplication::notify (this=0xbf94f868, receiver=0xba52ea8, e=0xc4aed98) at kernel/qapplication.cpp:3604
#40 0xb6c733dd in KApplication::notify (this=0xbf94f868, receiver=0xba52ea8, event=0xc4aed98) at /build/buildd/kde4libs-4.2.95/kdeui/kernel/kapplication.cpp:302
#41 0xb5b907ab in QCoreApplication::notifyInternal (this=0xbf94f868, receiver=0xba52ea8, event=0xc4aed98) at kernel/qcoreapplication.cpp:610
#42 0xb5b91405 in QCoreApplicationPrivate::sendPostedEvents (receiver=0x0, event_type=0, data=0x9cd0c08) at ../../include/QtCore/../../src/corelib/kernel/qcoreapplication.h:213
#43 0xb5b915fd in QCoreApplication::sendPostedEvents (receiver=0x0, event_type=0) at kernel/qcoreapplication.cpp:1140
#44 0xb5bbc58f in postEventSourceDispatch (s=0x9cfa4d0) at ../../include/QtCore/../../src/corelib/kernel/qcoreapplication.h:218
#45 0xb4c64b88 in IA__g_main_context_dispatch (context=0x9cfa448) at /build/buildd/glib2.0-2.20.1/glib/gmain.c:1814
#46 0xb4c680eb in g_main_context_iterate (context=0x9cfa448, block=1, dispatch=1, self=0x9cf4d38) at /build/buildd/glib2.0-2.20.1/glib/gmain.c:2448
#47 0xb4c68268 in IA__g_main_context_iteration (context=0x9cfa448, may_block=1) at /build/buildd/glib2.0-2.20.1/glib/gmain.c:2511
#48 0xb5bbc1d8 in QEventDispatcherGlib::processEvents (this=0x9cf4fc0, flags={i = -1080756424}) at kernel/qeventdispatcher_glib.cpp:324
#49 0xb60f0765 in QGuiEventDispatcherGlib::processEvents (this=0x9cf4fc0, flags={i = -1080756376}) at kernel/qguieventdispatcher_glib.cpp:202
#50 0xb5b8edda in QEventLoop::processEvents (this=0xbf94f7e0, flags={i = -1080756312}) at kernel/qeventloop.cpp:149
#51 0xb5b8f21a in QEventLoop::exec (this=0xbf94f7e0, flags={i = -1080756248}) at kernel/qeventloop.cpp:200
#52 0xb5b916c9 in QCoreApplication::exec () at kernel/qcoreapplication.cpp:888
#53 0xb604ea47 in QApplication::exec () at kernel/qapplication.cpp:3526
#54 0x0804bfef in main (argc=1, argv=0xbf94fb64) at /build/buildd/kdepim-4.2.95a/kontact/src/main.cpp:218