Looks like you hovered the mouse over an URL in the message, and it crashed after that.

Can you reproduce the crash with the same message?

I've tried a few times but I can't reproduce this because I'm not exactly sure what I was doing when it crashed. I was mousing over to another desktop while kmail was in the process of sending an email I'd *just* sent when it happened, but I can't pin down exactly what caused it to happen. If it's any help I think it happened while kmail was moving the message into the "Sent" folder on my IMAP server.

Thanks.

This has just happened to me again, very similar (to my uneducated eye) backtrace. 

I was scrolling the folder list when this happened but probably just moved the mouse pointer over the following URL which was the only URL visible in kmail when I did this. It was in the signature of an email.
--- cut url ---
Live Earth ‘07 updates, artist info & concert streams!
http://ninemsn.com.au/share/redir/adTrack.asp?mode=click&clientID=790&referral=windowslivehotmailtagline&URL=http://liveearth.ninemsn.com.au
--- cut url ---

Backtrace follows:

Using host libthread_db library "/lib/tls/i686/cmov/libthread_db.so.1".
[Thread debugging using libthread_db enabled]
[New Thread -1250900272 (LWP 6181)]
[New Thread -1282143344 (LWP 6235)]
[New Thread -1273750640 (LWP 6234)]
[New Thread -1265357936 (LWP 6233)]
[New Thread -1256965232 (LWP 6232)]
[KCrash handler]
#6  0xb7dc1896 in KMMessage::bodyPart (aDwBodyPart=0x8b44c70, 
    aPart=0x8b7cd54, withBody=true)
    at /root/kdepim/new/kdepim-3.5.7/./mimelib/mimelib/string.h:618
#7  0xb7dc2af7 in (anonymous namespace)::AttachmentURLHandler::statusBarMessage (this=0x8aa2cf0, url=@0xbf8ddf24, w=0x867b080)
    at /root/kdepim/new/kdepim-3.5.7/./kmail/partNode.h:98
#8  0xb7c09149 in KMail::URLHandlerManager::statusBarMessage (this=0x8bb4f88, 
    url=@0xbf8ddf24, w=0x867b080)
    at /root/kdepim/new/kdepim-3.5.7/./kmail/urlhandlermanager.cpp:312
#9  0xb7d89fa9 in KMReaderWin::slotUrlOn (this=0x867b080, aUrl=@0x829f748)
    at /root/kdepim/new/kdepim-3.5.7/./kmail/kmreaderwin.cpp:1871
#10 0xb7e2b166 in KMReaderWin::qt_invoke (this=0x867b080, _id=58, 
    _o=0xbf8de088) at ./kmreaderwin.moc:292
#11 0xb6ffb88b in QObject::activate_signal (this=0x866f328, clist=0x86b5978, 
    o=0xbf8de088) at kernel/qobject.cpp:2356
#12 0xb6ffbdc0 in QObject::activate_signal (this=0x866f328, signal=8, 
    param=@0xbf8de0dc) at kernel/qobject.cpp:2451
#13 0xb6268630 in KHTMLPart::onURL (this=0x866f328, t0=@0x86c68c0)
    at ./khtml_part.moc:409
#14 0xb62719fd in KHTMLPart::overURL (this=0x866f328, url=@0x86c68c0, 
    target=@0xbf8de9b8)
    at /root/kdelibs/kdelibs-3.5.7/./khtml/khtml_part.cpp:3726
#15 0xb629577e in KHTMLPart::khtmlMouseMoveEvent (this=0x866f328, 
    event=0xbf8ded24)
    at /root/kdelibs/kdelibs-3.5.7/./khtml/khtml_part.cpp:6482
#16 0xb6253d10 in KHTMLPart::customEvent (this=0x866f328, event=0xbf8ded24)
    at /root/kdelibs/kdelibs-3.5.7/./khtml/khtml_part.cpp:5954
#17 0xb6ffaf8d in QObject::event (this=0x866f328, e=0xbf8ded24)
    at kernel/qobject.cpp:755
#18 0xb6f92a60 in QApplication::internalNotify (this=0xbf8dfa74, 
    receiver=0x866f328, e=0xbf8ded24) at kernel/qapplication.cpp:2635
#19 0xb6f9488f in QApplication::notify (this=0xbf8dfa74, receiver=0x866f328, 
    e=0xbf8ded24) at kernel/qapplication.cpp:2358
#20 0xb76cec32 in KApplication::notify (this=0xbf8dfa74, receiver=0x866f328, 
    event=0xbf8ded24)
    at /root/kdelibs/kdelibs-3.5.7/./kdecore/kapplication.cpp:550
#21 0xb628edf2 in KHTMLView::viewportMouseMoveEvent (this=0x86b2aa8, 
    _mouse=0xbf8df420) at /usr/share/qt3/include/qapplication.h:520
#22 0xb7132522 in QScrollView::eventFilter (this=0x86b2aa8, obj=0x86bf440, 
    e=0xbf8df420) at widgets/qscrollview.cpp:1511
#23 0xb626b449 in KHTMLView::eventFilter (this=0x86b2aa8, o=0x86bf440, 
    e=0xbf8df420) at /root/kdelibs/kdelibs-3.5.7/./khtml/khtmlview.cpp:1976
#24 0xb6ffae38 in QObject::activate_filters (this=0x86bf440, e=0xbf8df420)
    at kernel/qobject.cpp:903
#25 0xb6ffaeb6 in QObject::event (this=0x86bf440, e=0xbf8df420)
    at kernel/qobject.cpp:735
#26 0xb703258f in QWidget::event (this=0x86bf440, e=0xbf8df420)
    at kernel/qwidget.cpp:4678
#27 0xb6f92a60 in QApplication::internalNotify (this=0xbf8dfa74, 
    receiver=0x86bf440, e=0xbf8df420) at kernel/qapplication.cpp:2635
#28 0xb6f94c1e in QApplication::notify (this=0xbf8dfa74, receiver=0x86bf440, 
    e=0xbf8df420) at kernel/qapplication.cpp:2421
#29 0xb76cec32 in KApplication::notify (this=0xbf8dfa74, receiver=0x86bf440, 
    event=0xbf8df420)
    at /root/kdelibs/kdelibs-3.5.7/./kdecore/kapplication.cpp:550
#30 0xb6f2525d in QApplication::sendSpontaneousEvent (receiver=0x86bf440, 
    event=0xbf8df420) at kernel/qapplication.h:523
#31 0xb6f23ec2 in QETWidget::translateMouseEvent (this=0x86bf440, 
    event=0xbf8df878) at kernel/qapplication_x11.cpp:4303
#32 0xb6f21fac in QApplication::x11ProcessEvent (this=0xbf8dfa74, 
    event=0xbf8df878) at kernel/qapplication_x11.cpp:3480
#33 0xb6f39180 in QEventLoop::processEvents (this=0x8070678, flags=4)
    at kernel/qeventloop_x11.cpp:192
#34 0xb6fad136 in QEventLoop::enterLoop (this=0x8070678)
    at kernel/qeventloop.cpp:198
#35 0xb6facf46 in QEventLoop::exec (this=0x8070678)
    at kernel/qeventloop.cpp:145
#36 0xb6f94609 in QApplication::exec (this=0xbf8dfa74)
    at kernel/qapplication.cpp:2758
#37 0x0804a2de in main (argc=)
    at /root/kdepim/new/kdepim-3.5.7/./kmail/main.cpp:110
#38 0xb7768ebc in __libc_start_main () from /lib/tls/i686/cmov/libc.so.6
#39 0x0804a041 in _start ()

I just got the same crash when hovering the mouse over the URL of a PDF attachment. I am running Debian's kmail 4:3.5.7-4.

*** This bug has been marked as a duplicate of 128357 ***