Here's another backtrace, not sure if I was clicking on delete in that exact moment: 

Application: KMail (kmail), signal SIGSEGV
[Thread debugging using libthread_db enabled]
[New Thread 0xb8081770 (LWP 9749)]
[KCrash handler]
#6  0x02f6954a in QDrag::target () from /usr/lib/libQtGui.so.4
#7  0x041c0b69 in Q3DragObject::drag () from /usr/lib/libQt3Support.so.4
#8  0x04486a64 in K3ListView::startDrag (this=<value optimized out>)
    at /usr/src/debug/kdelibs-4.1.0/kde3support/kdeui/k3listview.cpp:1145
#9  0x04487373 in K3ListView::contentsMouseMoveEvent (
    this=<value optimized out>, e=<value optimized out>)
    at /usr/src/debug/kdelibs-4.1.0/kde3support/kdeui/k3listview.cpp:827
#10 0x0425f7d1 in Q3ScrollView::viewportMouseMoveEvent ()
   from /usr/lib/libQt3Support.so.4
#11 0x04261592 in Q3ScrollView::eventFilter ()
   from /usr/lib/libQt3Support.so.4
#12 0x041fce56 in Q3ListView::eventFilter () from /usr/lib/libQt3Support.so.4
#13 0x04ebeefa in KMFolderTree::eventFilter (this=<value optimized out>, 
    o=<value optimized out>, e=<value optimized out>)
    at /usr/src/debug/kdepim-4.1.0/kmail/kmfoldertree.cpp:1811
#14 0x07aeb91a in QCoreApplicationPrivate::sendThroughObjectEventFilters ()
   from /usr/lib/libQtCore.so.4
#15 0x02f562ea in QApplicationPrivate::notify_helper ()
   from /usr/lib/libQtGui.so.4
#16 0x02f5eb21 in QApplication::notify () from /usr/lib/libQtGui.so.4
#17 0x038dbddd in KApplication::notify (this=<value optimized out>, 
    receiver=<value optimized out>, event=<value optimized out>)
    at /usr/src/debug/kdelibs-4.1.0/kdeui/kernel/kapplication.cpp:311
#18 0x07aec731 in QCoreApplication::notifyInternal ()
   from /usr/lib/libQtCore.so.4
#19 0x02f5ddae in QApplicationPrivate::sendMouseEvent ()
   from /usr/lib/libQtGui.so.4
#20 0x02fc7e16 in ?? () from /usr/lib/libQtGui.so.4
#21 0x02fc7185 in QApplication::x11ProcessEvent () from /usr/lib/libQtGui.so.4
#22 0x02fef6cc in ?? () from /usr/lib/libQtGui.so.4
#23 0x0061d0d8 in g_main_context_dispatch () from /lib/libglib-2.0.so.0
#24 0x00620783 in ?? () from /lib/libglib-2.0.so.0
#25 0x00620941 in g_main_context_iteration () from /lib/libglib-2.0.so.0
#26 0x07b16ea8 in QEventDispatcherGlib::processEvents ()
   from /usr/lib/libQtCore.so.4
#27 0x02feed95 in ?? () from /usr/lib/libQtGui.so.4
#28 0x07aeae1a in QEventLoop::processEvents () from /usr/lib/libQtCore.so.4
#29 0x07aeafda in QEventLoop::exec () from /usr/lib/libQtCore.so.4
#30 0x07aed685 in QCoreApplication::exec () from /usr/lib/libQtCore.so.4
#31 0x02f56187 in QApplication::exec () from /usr/lib/libQtGui.so.4
#32 0x0804a630 in main (argc=1, argv=0x2)
    at /usr/src/debug/kdepim-4.1.0/kmail/main.cpp:146

Another one during shutdown:
Application: KMail (kmail), signal SIGSEGV
[Thread debugging using libthread_db enabled]
[New Thread 0xb7ee2770 (LWP 15577)]
[KCrash handler]
#6  0x04e2553a in KMMessage::transferInProgress (this=)
    at /usr/src/debug/kdepim-4.1.0/kmail/kmmessage.cpp:268
#7  0x04fedcd0 in KMAcctImap::killAllJobs (this=<value optimized out>, 
    disconnectSlave=<value optimized out>)
    at /usr/src/debug/kdepim-4.1.0/kmail/kmacctimap.cpp:161
#8  0x04fee11f in ~KMAcctImap (this=<value optimized out>)
    at /usr/src/debug/kdepim-4.1.0/kmail/kmacctimap.cpp:87
#9  0x04f78bee in ~AccountManager (this=<value optimized out>)
    at /usr/include/QtCore/qalgorithms.h:352
#10 0x0504a54e in KMKernel::cleanup (this=<value optimized out>)
    at /usr/src/debug/kdepim-4.1.0/kmail/kmkernel.cpp:1688
#11 0x0804a63a in main (argc=1, argv=0x3)
    at /usr/src/debug/kdepim-4.1.0/kmail/main.cpp:148

Dunno why I happens so often now :-)

Here's another one after deleting messages.
The backtrace from the previous comment happend while i closed kmail.

Application: KMail (kmail), signal SIGSEGV
[Thread debugging using libthread_db enabled]
[New Thread 0xb8073770 (LWP 16465)]
[KCrash handler]
#6  0x00000000 in ?? ()
#7  0x04e25540 in KMMessage::transferInProgress (this=)
    at /usr/src/debug/kdepim-4.1.0/kmail/kmmessage.cpp:268
#8  0x0514a21c in KMail::ImapJob::slotGetMessageResult (
    this=<value optimized out>, job=<value optimized out>)
    at /usr/src/debug/kdepim-4.1.0/kmail/imapjob.cpp:374
#9  0x0514f474 in KMail::ImapJob::qt_metacall (this=<value optimized out>, 
    _c=<value optimized out>, _id=<value optimized out>, 
    _a=<value optimized out>)
    at /usr/src/debug/kdepim-4.1.0/i386-redhat-linux-gnu/kmail/imapjob.moc:81
#10 0x07b013e0 in QMetaObject::activate () from /usr/lib/libQtCore.so.4
#11 0x07b02162 in QMetaObject::activate () from /usr/lib/libQtCore.so.4
#12 0x07d9cc03 in KJob::result (this=)
    at /usr/src/debug/kdelibs-4.1.0/i386-redhat-linux-gnu/kdecore/kjob.moc:186
#13 0x07d9d0a2 in KJob::emitResult (this=<value optimized out>)
    at /usr/src/debug/kdelibs-4.1.0/kdecore/jobs/kjob.cpp:290
#14 0x03bdac55 in KIO::SimpleJob::slotFinished (this=<value optimized out>)
    at /usr/src/debug/kdelibs-4.1.0/kio/kio/job.cpp:498
#15 0x03bdb7e3 in KIO::TransferJob::slotFinished (this=<value optimized out>)
    at /usr/src/debug/kdelibs-4.1.0/kio/kio/job.cpp:967
#16 0x03bdc86b in KIO::TransferJob::qt_metacall (this=<value optimized out>, 
    _c=<value optimized out>, _id=<value optimized out>, 
    _a=<value optimized out>)
    at /usr/src/debug/kdelibs-4.1.0/i386-redhat-linux-gnu/kio/jobclasses.moc:336
#17 0x07b013e0 in QMetaObject::activate () from /usr/lib/libQtCore.so.4
#18 0x07b02162 in QMetaObject::activate () from /usr/lib/libQtCore.so.4
#19 0x03c86fd7 in KIO::SlaveInterface::finished (this=)
    at /usr/src/debug/kdelibs-4.1.0/i386-redhat-linux-gnu/kio/slaveinterface.moc:161
#20 0x03c89b4f in KIO::SlaveInterface::dispatch (this=<value optimized out>, 
    _cmd=<value optimized out>, rawdata=<value optimized out>)
    at /usr/src/debug/kdelibs-4.1.0/kio/kio/slaveinterface.cpp:175
#21 0x03c87887 in KIO::SlaveInterface::dispatch (this=<value optimized out>)
    at /usr/src/debug/kdelibs-4.1.0/kio/kio/slaveinterface.cpp:90
#22 0x03c7a500 in KIO::Slave::gotInput (this=<value optimized out>)
    at /usr/src/debug/kdelibs-4.1.0/kio/kio/slave.cpp:319
#23 0x03c7a873 in KIO::Slave::qt_metacall (this=<value optimized out>, 
    _c=<value optimized out>, _id=<value optimized out>, 
    _a=<value optimized out>)
    at /usr/src/debug/kdelibs-4.1.0/i386-redhat-linux-gnu/kio/slave.moc:75
#24 0x07b013e0 in QMetaObject::activate () from /usr/lib/libQtCore.so.4
#25 0x07b02162 in QMetaObject::activate () from /usr/lib/libQtCore.so.4
#26 0x03baa877 in KIO::Connection::readyRead (this=)
    at /usr/src/debug/kdelibs-4.1.0/i386-redhat-linux-gnu/kio/connection.moc:84
#27 0x03bac2a3 in KIO::ConnectionPrivate::dequeue (this=<value optimized out>)
    at /usr/src/debug/kdelibs-4.1.0/kio/kio/connection.cpp:82
#28 0x03bac8f6 in KIO::Connection::qt_metacall (this=<value optimized out>, 
    _c=<value optimized out>, _id=<value optimized out>, 
    _a=<value optimized out>)
    at /usr/src/debug/kdelibs-4.1.0/i386-redhat-linux-gnu/kio/connection.moc:72
#29 0x07afa53b in QMetaCallEvent::placeMetaCall ()
   from /usr/lib/libQtCore.so.4
#30 0x07afc0f9 in QObject::event () from /usr/lib/libQtCore.so.4
#31 0x02f5630c in QApplicationPrivate::notify_helper ()
   from /usr/lib/libQtGui.so.4
#32 0x02f5e16e in QApplication::notify () from /usr/lib/libQtGui.so.4
#33 0x038dbddd in KApplication::notify (this=<value optimized out>, 
    receiver=<value optimized out>, event=<value optimized out>)
    at /usr/src/debug/kdelibs-4.1.0/kdeui/kernel/kapplication.cpp:311
#34 0x07aec731 in QCoreApplication::notifyInternal ()
   from /usr/lib/libQtCore.so.4
#35 0x07aed3a5 in QCoreApplicationPrivate::sendPostedEvents ()
   from /usr/lib/libQtCore.so.4
#36 0x07aed5bd in QCoreApplication::sendPostedEvents ()
   from /usr/lib/libQtCore.so.4
#37 0x07b1725f in ?? () from /usr/lib/libQtCore.so.4
#38 0x0061d0d8 in g_main_context_dispatch () from /lib/libglib-2.0.so.0
#39 0x00620783 in ?? () from /lib/libglib-2.0.so.0
#40 0x00620941 in g_main_context_iteration () from /lib/libglib-2.0.so.0
#41 0x07b16ea8 in QEventDispatcherGlib::processEvents ()
   from /usr/lib/libQtCore.so.4
#42 0x02feed95 in ?? () from /usr/lib/libQtGui.so.4
#43 0x07aeae1a in QEventLoop::processEvents () from /usr/lib/libQtCore.so.4
#44 0x07aeafda in QEventLoop::exec () from /usr/lib/libQtCore.so.4
#45 0x07aed685 in QCoreApplication::exec () from /usr/lib/libQtCore.so.4
#46 0x02f56187 in QApplication::exec () from /usr/lib/libQtGui.so.4
#47 0x0804a630 in main (argc=88473928, argv=0x9580348)
    at /usr/src/debug/kdepim-4.1.0/kmail/main.cpp:146

Hope it's useful. I'll post them only if they look "different" than the previous ones to me.

Confirmed on 1.10.1 (kde 4.1.2). Please, tell me if you want a full backtrace.

I could reproduce on kmail 1.11.2 even without closing kmail. Keep deleting spam mails on gmail imap account to reproduce.

Backtrace:

Application: KMail (kmail), signal SIGSEGV
[?1034h[Thread debugging using libthread_db enabled]
[Current thread is 1 (Thread 0xb3c53700 (LWP 19734))]

Thread 1 (Thread 0xb3c53700 (LWP 19734)):
[KCrash Handler]
#6  KMail::FolderJob::msgList (this=0x28) at /usr/include/QtCore/qlist.h:107
#7  0xb756c73b in KMAcctImap::ignoreJobsForMessage (this=0x85a6ef0, msg=0x8c7da00) at /usr/src/debug/kdepim-4.2.2/kmail/kmacctimap.cpp:215
#8  0xb7580ee5 in KMFolderImap::ignoreJobsForMessage (this=0x8373f38, msg=0x8c7da00) at /usr/src/debug/kdepim-4.2.2/kmail/kmfolderimap.cpp:1562
#9  0xb767a814 in KMMoveCommand::execute (this=0x8ce6ba0) at /usr/src/debug/kdepim-4.2.2/kmail/kmcommands.cpp:2086
#10 0xb7668c12 in KMCommand::slotPostTransfer (this=0x8ce6ba0, result=KMCommand::OK) at /usr/src/debug/kdepim-4.2.2/kmail/kmcommands.cpp:276
#11 0xb7672d94 in KMCommand::qt_metacall (this=0x8ce6ba0, _c=QMetaObject::InvokeMetaMethod, _id=5, _a=0xbfd972dc) at /usr/src/debug/kdepim-4.2.2/build/kmail/kmcommands.moc:86
#12 0xb767328a in KMMoveCommand::qt_metacall (this=0x8ce6ba0, _c=QMetaObject::InvokeMetaMethod, _id=9, _a=0xbfd972dc) at /usr/src/debug/kdepim-4.2.2/build/kmail/kmcommands.moc:1662
#13 0xb7673352 in KMDeleteMsgCommand::qt_metacall (this=0x8ce6ba0, _c=QMetaObject::InvokeMetaMethod, _id=9, _a=0xbfd972dc) at /usr/src/debug/kdepim-4.2.2/build/kmail/kmcommands.moc:1712
#14 0xb6b91c88 in QMetaObject::activate (sender=0x8ce6ba0, from_signal_index=4, to_signal_index=4, argv=0xbfd972dc) at kernel/qobject.cpp:3069
#15 0xb6b93412 in QMetaObject::activate (sender=0x8ce6ba0, m=0xb7a599d4, local_signal_index=0, argv=0xbfd972dc) at kernel/qobject.cpp:3143
#16 0xb7664773 in KMCommand::messagesTransfered (this=0x8ce6ba0, _t1=KMCommand::OK) at /usr/src/debug/kdepim-4.2.2/build/kmail/kmcommands.moc:100
#17 0xb767cb94 in KMCommand::transferSelectedMsgs (this=0x8ce6ba0) at /usr/src/debug/kdepim-4.2.2/kmail/kmcommands.cpp:370
#18 0xb767cd83 in KMCommand::slotStart (this=0x8ce6ba0) at /usr/src/debug/kdepim-4.2.2/kmail/kmcommands.cpp:268
#19 0xb7672da3 in KMCommand::qt_metacall (this=0x8ce6ba0, _c=QMetaObject::InvokeMetaMethod, _id=4, _a=0xbfd974d8) at /usr/src/debug/kdepim-4.2.2/build/kmail/kmcommands.moc:85
#20 0xb767328a in KMMoveCommand::qt_metacall (this=0x8ce6ba0, _c=QMetaObject::InvokeMetaMethod, _id=8, _a=0xbfd974d8) at /usr/src/debug/kdepim-4.2.2/build/kmail/kmcommands.moc:1662
#21 0xb7673352 in KMDeleteMsgCommand::qt_metacall (this=0x8ce6ba0, _c=QMetaObject::InvokeMetaMethod, _id=8, _a=0xbfd974d8) at /usr/src/debug/kdepim-4.2.2/build/kmail/kmcommands.moc:1712
#22 0xb6b91c88 in QMetaObject::activate (sender=0x8b66908, from_signal_index=4, to_signal_index=4, argv=0x0) at kernel/qobject.cpp:3069
#23 0xb6b93412 in QMetaObject::activate (sender=0x8b66908, m=0xb6c71908, local_signal_index=0, argv=0x0) at kernel/qobject.cpp:3143
#24 0xb6b970f7 in QSingleShotTimer::timeout (this=0x8b66908) at .moc/release-shared/qtimer.moc:76
#25 0xb6b9721c in QSingleShotTimer::timerEvent (this=0x8b66908) at kernel/qtimer.cpp:298
#26 0xb6b8c12f in QObject::event (this=0x8b66908, e=0xbfd97980) at kernel/qobject.cpp:1082
#27 0xb602beec in QApplicationPrivate::notify_helper (this=0x807d0a0, receiver=0x8b66908, e=0xbfd97980) at kernel/qapplication.cpp:4084
#28 0xb60341ae in QApplication::notify (this=0xbfd97cc8, receiver=0x8b66908, e=0xbfd97980) at kernel/qapplication.cpp:3631
#29 0xb7e65ded in KApplication::notify (this=0xbfd97cc8, receiver=0x8b66908, event=0xbfd97980) at /usr/src/debug/kdelibs-4.2.2/kdeui/kernel/kapplication.cpp:307
#30 0xb6b7b9db in QCoreApplication::notifyInternal (this=0xbfd97cc8, receiver=0x8b66908, event=0xbfd97980) at kernel/qcoreapplication.cpp:602
#31 0xb6bab026 in QTimerInfoList::activateTimers (this=0x807fc34) at kernel/qcoreapplication.h:213
#32 0xb6ba74d0 in timerSourceDispatch (source=0x807fc00) at kernel/qeventdispatcher_glib.cpp:164
#33 0xb43fcd88 in IA__g_main_context_dispatch (context=0x807f090) at gmain.c:1814
#34 0xb44002fb in g_main_context_iterate (context=0x807f090, block=1, dispatch=1, self=0x807ce18) at gmain.c:2448
#35 0xb4400478 in IA__g_main_context_iteration (context=0x807f090, may_block=1) at gmain.c:2511
#36 0xb6ba7428 in QEventDispatcherGlib::processEvents (this=0x805d8d0, flags={i = -1076266200}) at kernel/qeventdispatcher_glib.cpp:323
#37 0xb60cbac5 in QGuiEventDispatcherGlib::processEvents (this=0x805d8d0, flags={i = -1076266152}) at kernel/qguieventdispatcher_glib.cpp:202
#38 0xb6b79ffa in QEventLoop::processEvents (this=0xbfd97bd0, flags={i = -1076266088}) at kernel/qeventloop.cpp:149
#39 0xb6b7a43a in QEventLoop::exec (this=0xbfd97bd0, flags={i = -1076266024}) at kernel/qeventloop.cpp:200
#40 0xb6b7c8e9 in QCoreApplication::exec () at kernel/qcoreapplication.cpp:880
#41 0xb602bd67 in QApplication::exec () at kernel/qapplication.cpp:3553
#42 0x0804a5e0 in main (argc=) at /usr/src/debug/kdepim-4.2.2/kmail/main.cpp:146

Description and comment #3 show similar backtraces.
Comments #1 and #2 show unrelated crashes.
Comment #5 shows another unrelated crash, a duplicate of bug 163071.

ok, as there are too many different backtraces in this report, I'll close with invalid.

Constantin gave clues about the different backtraces.
The backtrace in comment #1 won't happen anymore (no KDE3 code anymore in KMail).

The original one is probably a duplicate of bug 181611.