Application that crashed: kontact
Version of the application: 4.3.0 rc2
KDE Version: 4.2.96 (KDE 4.2.96 (KDE 4.3 RC2))
Qt Version: 4.5.2
Operating System: Linux 2.6.28-13-generic x86_64
Distribution: Ubuntu karmic (development branch)

What I was doing when the application crashed:
Hope this is of some help. aMsg looks to be corrupted / deleted / uninitialized to me...

#5  0x00007f162b2308b7 in KMReaderWin::parseMsg (this=0x21b3f10, aMsg=0x347a8c0) at ../../kmail/kmreaderwin.cpp:1662                                                                               
(gdb) p *this
$3 = {<QWidget> = {<QObject> = {_vptr.QObject = 0x7f162b9cc510, d_ptr = 0x21b4150}, <QPaintDevice> = {_vptr.QPaintDevice = 0x7f162b9cc708, painters = 0}, data = 0x21b41d8}, <KMail::Interface::Observer> = {_vptr.Observer = 0x7f162b9cc740}, mHtmlMail = false,
  mHtmlLoadExternal = false, mHtmlOverride = false, mHtmlLoadExtOverride = false, mAtmCurrent = 0, mAtmCurrentName = {d = 0x6064a0}, mMessage = 0x0, mSplitter = 0x21b4900, mBox = 0x21bd030, mColorBar = 0x21bcd80, mMimePartTree = 0x21b4ce0, mViewer = 0x21be050,
  mAttachmentStrategy = 0x22591f0, mHeaderStrategy = 0x1e8ac00, mHeaderStyle = 0x2259170, mAutoDelete = false, mSaveAttachDir = {d = 0x6064a0}, mUpdateReaderWinTimer = {<QObject> = {_vptr.QObject = 0x7f1648abd2d0, d_ptr = 0x21b4390}, id = -1, inter = 0, del = 0, single = 1,
    nulltimer = 1}, mResizeTimer = {<QObject> = {_vptr.QObject = 0x7f1648abd2d0, d_ptr = 0x21b4420}, id = -1, inter = 100, del = 0, single = 1, nulltimer = 0}, mDelayedMarkTimer = {<QObject> = {_vptr.QObject = 0x7f1648abd2d0, d_ptr = 0x21b44b0}, id = -1, inter = 0, del = 0,
    single = 1, nulltimer = 0}, mOverrideEncoding = {d = 0x6064a0}, mOldGlobalOverrideEncoding = {d = 0x7f1648abe840}, mMsgDisplay = true, mNoMDNsWhenEncrypted = true, mLastSerNum = 492182, mLastStatus = {mStatus = 33028}, mCSSHelper = 0x2259530, mUseFixedFont = true,
  mPrinting = false, mShowColorbar = true, mTempFiles = {<QList<QString>> = {{p = {d = 0x7f1648abe780}, d = 0x7f1648abe780}}, <No data fields>}, mTempDirs = {<QList<QString>> = {{p = {d = 0x7f1648abe780}, d = 0x7f1648abe780}}, <No data fields>}, mMimeTreeMode = 1,
  mMimeTreeAtBottom = false, mSplitterSizes = {{p = {d = 0x21b46a0}, d = 0x21b46a0}}, mRootNode = 0x38646c0, mIdOfLastViewedMessage = {d = 0x6064a0}, mMainWindow = 0x218fea0, mActionCollection = 0x1657200, mMailToComposeAction = 0x2246720, mMailToReplyAction = 0x22516f0,
  mMailToForwardAction = 0x2251e70, mAddAddrBookAction = 0x2252a50, mOpenAddrBookAction = 0x2253230, mCopyAction = 0x22539b0, mCopyURLAction = 0x2254b00, mUrlOpenAction = 0x2255270, mUrlSaveAsAction = 0x2256120, mAddBookmarksAction = 0x2255a40, mSelectAllAction = 0x22542a0,
  mScrollUpAction = 0x2256980, mScrollDownAction = 0x22576d0, mScrollUpMoreAction = 0x2233520, mScrollDownMoreAction = 0x22587f0, mSelectEncodingAction = 0x2234300, mToggleFixFontAction = 0x22567f0, mUrlClicked = {<QUrl> = {d = 0x21b4540}, d = 0x0}, mHtmlWriter = 0x2235950,
  mPartHtmlWriter = {o = 0x2235940}, mAtmUpdate = false, mChoice = 0, mWaitingForSerNum = 0, mSavedRelativePosition = 0, mLevelQuote = 2, mDecrytMessageOverwrite = false, mShowSignatureDetails = false, mShowAttachmentQuicklist = true, mExternalWindow = true}
(gdb) p *aMsg
$4 = {<KMMsgBase> = {_vptr.KMMsgBase = 0x1600000002, mParent = 0x16, mIndexOffset = 55027930, mIndexLength = 22336, mDirty = 90, mEnableUndo = false, mStatus = {mStatus = 4325452}, mTagList = 0x46007600350045, mCachedStringParts = {{d = 0x30005900340054}, {
        d = 0x4d002b00660072}, {d = 0x4c0039002b0049}, {d = 0x6700520058}, {d = 0x746e656d6567}, {d = 0x60}, {d = 0x51}, {d = 0xd00000002}, {d = 0x7f160000000d}, {d = 0x347a93a}, {d = 0x63006900524540}, {d = 0x64007200610068}, {d = 0x69006d00530020}, {d = 0x57000000680074}, {
        d = 0x7100740078002b}, {d = 0x5100320033}, {d = 0x31}, {d = 0x3893880}, {d = 0x89969a7}, {d = 0x34cd7d0}}, mStringPartCacheBuilt = 16}, <KMail::ISubject> = {<KMail::Interface::Observable> = {_vptr.Observable = 0x4900200074006e}, mObserverList = {{p = 0x31, d = 0x31}}},
  mDrafts = {d = 0x31a10a0}, mTemplates = {d = 0xfb568b7}, mMsg = 0x37bb4a0, mNeedsAssembly = false, mDecodeHTML = false, mReadyToShow = false, mComplete = false, mIsParsed = true, mOverrideCodec = 0x30, mFileName = {d = 0x31}, mFolderOffset = 57644752, mMsgSize = 420868,
  mMsgLength = 58631632, mDate = 47575024, mEncryptionState = 2147483664, mSignatureState = 0, mMDNSentState = 33, mUnencryptedMsg = 0x7f1648abe780, mLastUpdated = 0x0, mCursorPos = 1}


 -- Backtrace:
Application: Kontact (kontact), signal: Segmentation fault
[KCrash Handler]
#5  0x00007f162b2308b7 in KMReaderWin::parseMsg (this=0x21b3f10, aMsg=0x347a8c0) at ../../kmail/kmreaderwin.cpp:1662
#6  0x00007f162b22002a in KMReaderWin::displayMessage (this=0x21b3f10) at ../../kmail/kmreaderwin.cpp:1589
#7  0x00007f162b220204 in KMReaderWin::updateReaderWin (this=0x21b3f10) at ../../kmail/kmreaderwin.cpp:1529
#8  0x00007f162b22be3d in KMReaderWin::qt_metacall (this=0x21b3f10, _c=QMetaObject::InvokeMetaMethod, _id=<value optimized out>, _a=0x7fff52ac0240) at ./kmreaderwin.moc:165
#9  0x00007f16487e2e1c in QMetaObject::activate (sender=0x21b3fa8, from_signal_index=<value optimized out>, to_signal_index=<value optimized out>, argv=0x3c64340) at kernel/qobject.cpp:3113
#10 0x00007f16487dcdc3 in QObject::event (this=0x21b3fa8, e=0x4e) at kernel/qobject.cpp:1075
#11 0x00007f16490e762c in QApplicationPrivate::notify_helper (this=0xff18e0, receiver=0x21b3fa8, e=0x7fff52ac0840) at kernel/qapplication.cpp:4056
#12 0x00007f16490ee8fe in QApplication::notify (this=0x7fff52ac0ba0, receiver=0x21b3fa8, e=0x7fff52ac0840) at kernel/qapplication.cpp:4021
#13 0x00007f1649d1d3f6 in KApplication::notify (this=0x7fff52ac0ba0, receiver=0x21b3fa8, event=0x7fff52ac0840) at ../../kdeui/kernel/kapplication.cpp:302
#14 0x00007f16487cdc6c in QCoreApplication::notifyInternal (this=0x7fff52ac0ba0, receiver=0x21b3fa8, event=0x7fff52ac0840) at kernel/qcoreapplication.cpp:610
#15 0x00007f16487f8912 in QCoreApplication::sendEvent (this=0xfea290) at ../../include/QtCore/../../src/corelib/kernel/qcoreapplication.h:213
#16 QTimerInfoList::activateTimers (this=0xfea290) at kernel/qeventdispatcher_unix.cpp:572
#17 0x00007f16487f62ad in timerSourceDispatch (source=<value optimized out>) at kernel/qeventdispatcher_glib.cpp:165
#18 0x00007f16425d79fe in g_main_context_dispatch () from /usr/lib/libglib-2.0.so.0
#19 0x00007f16425db3c8 in ?? () from /usr/lib/libglib-2.0.so.0
#20 0x00007f16425db4f0 in g_main_context_iteration () from /usr/lib/libglib-2.0.so.0
#21 0x00007f16487f61f6 in QEventDispatcherGlib::processEvents (this=0xfbfae0, flags=<value optimized out>) at kernel/qeventdispatcher_glib.cpp:327
#22 0x00007f164917bace in QGuiEventDispatcherGlib::processEvents (this=0x347a8c0, flags=<value optimized out>) at kernel/qguieventdispatcher_glib.cpp:202
#23 0x00007f16487cc572 in QEventLoop::processEvents (this=<value optimized out>, flags=) at kernel/qeventloop.cpp:149
#24 0x00007f16487cc944 in QEventLoop::exec (this=0x7fff52ac0ae0, flags=) at kernel/qeventloop.cpp:201
#25 0x00007f16487ceaf9 in QCoreApplication::exec () at kernel/qcoreapplication.cpp:888
#26 0x0000000000403f27 in main (argc=<value optimized out>, argv=<value optimized out>) at ../../../kontact/src/main.cpp:218

Reported using DrKonqi