KMail: Version 4.14.8
QT: 4.8.6-r2

After importing a lot of older emails, I found out that the maildir structure was missing most or all of the imported emails and their folders:

    $ ls -al local-mail/.Computer.directory/
    total 12
    drwxr-xr-x  3 daniel daniel 4096 Dec 13 15:20 .
    drwxr-xr-x 25 daniel daniel 4096 Dec 13 21:27 ..
    drwxr-xr-x  5 daniel daniel 4096 Dec 13 15:20 new

So I tried to at least create a backup by archiving all local folders.  This went fine for about half the messages (measured by the resulting file size), then KMail crashed.  A stack trace follows:

Application: Kontact (kontact), signal: Aborted
Using host libthread_db library "/lib64/libthread_db.so.1".
[Current thread is 1 (Thread 0x7ff79dba97c0 (LWP 24827))]

Thread 4 (Thread 0x7ff78651c700 (LWP 24830)):
#0  0x00007ff7959a986f in pthread_cond_wait () from /lib64/libpthread.so.0
#1  0x00007ff799319f06 in WTF::TCMalloc_PageHeap::scavengerThread() () from /usr/lib64/qt4/libQtWebKit.so.4
#2  0x00007ff799319f39 in WTF::TCMalloc_PageHeap::runScavengerThread(void*) () from /usr/lib64/qt4/libQtWebKit.so.4
#3  0x00007ff7959a5464 in start_thread () from /lib64/libpthread.so.0
#4  0x00007ff79b16968d in clone () from /lib64/libc.so.6

Thread 3 (Thread 0x7ff785c1b700 (LWP 24831)):
#0  0x00007ff794dc537c in g_mutex_unlock () from /usr/lib64/libglib-2.0.so.0
#1  0x00007ff794d84a10 in g_main_context_check () from /usr/lib64/libglib-2.0.so.0
#2  0x00007ff794d84f08 in g_main_context_iterate.isra () from /usr/lib64/libglib-2.0.so.0
#3  0x00007ff794d85074 in g_main_context_iteration () from /usr/lib64/libglib-2.0.so.0
#4  0x00007ff79c5538de in QEventDispatcherGlib::processEvents(QFlags<QEventLoop::ProcessEventsFlag>) () from /usr/lib64/qt4/libQtCore.so.4
#5  0x00007ff79c525c77 in QEventLoop::processEvents(QFlags<QEventLoop::ProcessEventsFlag>) () from /usr/lib64/qt4/libQtCore.so.4
#6  0x00007ff79c525f3d in QEventLoop::exec(QFlags<QEventLoop::ProcessEventsFlag>) () from /usr/lib64/qt4/libQtCore.so.4
#7  0x00007ff79c42599f in QThread::exec() () from /usr/lib64/qt4/libQtCore.so.4
#8  0x00007ff79c42808f in QThreadPrivate::start(void*) () from /usr/lib64/qt4/libQtCore.so.4
#9  0x00007ff7959a5464 in start_thread () from /lib64/libpthread.so.0
#10 0x00007ff79b16968d in clone () from /lib64/libc.so.6

Thread 2 (Thread 0x7ff731674700 (LWP 28153)):
#0  0x00007ff7959a986f in pthread_cond_wait () from /lib64/libpthread.so.0
#1  0x00007ff73cfc170b in QTWTF::TCMalloc_PageHeap::scavengerThread() () from /usr/lib64/qt4/libQtScript.so.4
#2  0x00007ff73cfc1751 in QTWTF::TCMalloc_PageHeap::runScavengerThread(void*) () from /usr/lib64/qt4/libQtScript.so.4
#3  0x00007ff7959a5464 in start_thread () from /lib64/libpthread.so.0
#4  0x00007ff79b16968d in clone () from /lib64/libc.so.6

Thread 1 (Thread 0x7ff79dba97c0 (LWP 24827)):
[KCrash Handler]
#6  0x00007ff79b0b7cd7 in raise () from /lib64/libc.so.6
#7  0x00007ff79b0b9099 in abort () from /lib64/libc.so.6
#8  0x00007ff79b47dfbd in __gnu_cxx::__verbose_terminate_handler() () from /usr/lib/gcc/x86_64-pc-linux-gnu/4.9.3/libstdc++.so.6
#9  0x00007ff79b47be66 in __cxxabiv1::__terminate(void (*)()) () from /usr/lib/gcc/x86_64-pc-linux-gnu/4.9.3/libstdc++.so.6
#10 0x00007ff79b47beb1 in std::terminate() () from /usr/lib/gcc/x86_64-pc-linux-gnu/4.9.3/libstdc++.so.6
#11 0x00007ff79b47c105 in __cxa_rethrow () from /usr/lib/gcc/x86_64-pc-linux-gnu/4.9.3/libstdc++.so.6
#12 0x00007ff79c52612d in QEventLoop::exec(QFlags<QEventLoop::ProcessEventsFlag>) () from /usr/lib64/qt4/libQtCore.so.4
#13 0x00007ff79c52b1f9 in QCoreApplication::exec() () from /usr/lib64/qt4/libQtCore.so.4
#14 0x00000000004035d2 in main ()