And again, I had built debugging info for QT 5.5.1 prior to this one.

Application: Akonadi Resource (akonadi_imap_resource), signal: Aborted
Using host libthread_db library "/lib64/libthread_db.so.1".
[Current thread is 1 (Thread 0x7fa5de3817c0 (LWP 6728))]

Thread 4 (Thread 0x7fa5dcbae700 (LWP 6729)):
#0  0x00007fa5ecd2454d in poll () from /lib64/libc.so.6
#1  0x00007fa5e866aa12 in ?? () from /usr/lib64/libxcb.so.1
#2  0x00007fa5e866c6d7 in xcb_wait_for_event () from /usr/lib64/libxcb.so.1
#3  0x00007fa5de0bc189 in QXcbEventReader::run (this=0x201d790) at qxcbconnection.cpp:1229
#4  0x00007fa5ed5ae912 in QThreadPrivate::start (arg=0x201d790) at thread/qthread_unix.cpp:331
#5  0x00007fa5e888b4c6 in start_thread () from /lib64/libpthread.so.0
#6  0x00007fa5ecd2d86d in clone () from /lib64/libc.so.6

Thread 3 (Thread 0x7fa5d5e60700 (LWP 6732)):
#0  0x00007fa5e62a3ab6 in g_main_context_prepare () from /usr/lib64/libglib-2.0.so.0
#1  0x00007fa5e62a44e8 in ?? () from /usr/lib64/libglib-2.0.so.0
#2  0x00007fa5e62a46ec in g_main_context_iteration () from /usr/lib64/libglib-2.0.so.0
#3  0x00007fa5ed7b50eb in QEventDispatcherGlib::processEvents (this=0x7fa5d00008c0, flags=...) at kernel/qeventdispatcher_glib.cpp:418
#4  0x00007fa5ed764daa in QEventLoop::exec (this=this@entry=0x7fa5d5e5fe00, flags=..., flags@entry=...) at kernel/qeventloop.cpp:204
#5  0x00007fa5ed5a9cf6 in QThread::exec (this=<optimized out>) at thread/qthread.cpp:503
#6  0x00007fa5ed5ae912 in QThreadPrivate::start (arg=0x212d590) at thread/qthread_unix.cpp:331
#7  0x00007fa5e888b4c6 in start_thread () from /lib64/libpthread.so.0
#8  0x00007fa5ecd2d86d in clone () from /lib64/libc.so.6

Thread 2 (Thread 0x7fa5ce9d4700 (LWP 6741)):
#0  0x00007fa5ecd2454d in poll () from /lib64/libc.so.6
#1  0x00007fa5e62a45bc in ?? () from /usr/lib64/libglib-2.0.so.0
#2  0x00007fa5e62a46ec in g_main_context_iteration () from /usr/lib64/libglib-2.0.so.0
#3  0x00007fa5ed7b50eb in QEventDispatcherGlib::processEvents (this=0x7fa5c40008c0, flags=...) at kernel/qeventdispatcher_glib.cpp:418
#4  0x00007fa5ed764daa in QEventLoop::exec (this=this@entry=0x7fa5ce9d3e00, flags=..., flags@entry=...) at kernel/qeventloop.cpp:204
#5  0x00007fa5ed5a9cf6 in QThread::exec (this=<optimized out>) at thread/qthread.cpp:503
#6  0x00007fa5ed5ae912 in QThreadPrivate::start (arg=0x211b620) at thread/qthread_unix.cpp:331
#7  0x00007fa5e888b4c6 in start_thread () from /lib64/libpthread.so.0
#8  0x00007fa5ecd2d86d in clone () from /lib64/libc.so.6

Thread 1 (Thread 0x7fa5de3817c0 (LWP 6728)):
[KCrash Handler]
#6  0x00007fa5ecc76897 in raise () from /lib64/libc.so.6
#7  0x00007fa5ecc77cbd in abort () from /lib64/libc.so.6
#8  0x00007fa5ed25a745 in __gnu_cxx::__verbose_terminate_handler() () from /usr/lib/gcc/x86_64-pc-linux-gnu/4.9.3/libstdc++.so.6
#9  0x00007fa5ed258426 in ?? () from /usr/lib/gcc/x86_64-pc-linux-gnu/4.9.3/libstdc++.so.6
#10 0x00007fa5ed258491 in std::terminate() () from /usr/lib/gcc/x86_64-pc-linux-gnu/4.9.3/libstdc++.so.6
#11 0x00007fa5ed2586c7 in __cxa_throw () from /usr/lib/gcc/x86_64-pc-linux-gnu/4.9.3/libstdc++.so.6
#12 0x00007fa5ebf0d824 in operator<< <signed char> (val=<optimized out>, this=<optimized out>) at /tmp/portage/kde-apps/akonadi-15.08.2/work/akonadi-15.08.2/src/private/datastream_p_p.h:95
#13 operator<< <Akonadi::Protocol::TransactionCommand::Mode> (val=<optimized out>, this=<optimized out>) at /tmp/portage/kde-apps/akonadi-15.08.2/work/akonadi-15.08.2/src/private/datastream_p_p.h:104
#14 Akonadi::Protocol::TransactionCommandPrivate::serialize (this=<optimized out>, stream=...) at /tmp/portage/kde-apps/akonadi-15.08.2/work/akonadi-15.08.2/src/private/protocol.cpp:1796
#15 0x00007fa5ebef6c54 in operator<< (command=..., stream=...) at /tmp/portage/kde-apps/akonadi-15.08.2/work/akonadi-15.08.2/src/private/protocol.cpp:354
#16 Akonadi::Protocol::serialize (device=<optimized out>, command=...) at /tmp/portage/kde-apps/akonadi-15.08.2/work/akonadi-15.08.2/src/private/protocol.cpp:600
#17 0x00007fa5f03ff397 in Akonadi::SessionPrivate::sendCommand (this=0x2118c00, tag=105, command=...) at /tmp/portage/kde-apps/kdepimlibs-15.08.2/work/kdepimlibs-15.08.2/akonadi/src/core/session.cpp:399
#18 0x00007fa5f043dfc2 in Akonadi::JobPrivate::sendCommand (this=this@entry=0x22f7810, tag=<optimized out>, cmd=...) at /tmp/portage/kde-apps/kdepimlibs-15.08.2/work/kdepimlibs-15.08.2/akonadi/src/core/jobs/job.cpp:216
#19 0x00007fa5f043e005 in Akonadi::JobPrivate::sendCommand (this=this@entry=0x22f7810, cmd=...) at /tmp/portage/kde-apps/kdepimlibs-15.08.2/work/kdepimlibs-15.08.2/akonadi/src/core/jobs/job.cpp:222
#20 0x00007fa5f0458b8c in Akonadi::TransactionJob::doStart (this=<optimized out>) at /tmp/portage/kde-apps/kdepimlibs-15.08.2/work/kdepimlibs-15.08.2/akonadi/src/core/jobs/transactionjobs.cpp:62
#21 0x00007fa5f043de00 in Akonadi::JobPrivate::startQueued (this=<optimized out>) at /tmp/portage/kde-apps/kdepimlibs-15.08.2/work/kdepimlibs-15.08.2/akonadi/src/core/jobs/job.cpp:162
#22 0x00007fa5f043df2e in Akonadi::JobPrivate::startNext (this=<optimized out>) at /tmp/portage/kde-apps/kdepimlibs-15.08.2/work/kdepimlibs-15.08.2/akonadi/src/core/jobs/job.cpp:192
#23 0x00007fa5f043eb61 in Akonadi::Job::qt_static_metacall (_o=<optimized out>, _c=<optimized out>, _id=<optimized out>, _a=<optimized out>) at /tmp/portage/kde-apps/kdepimlibs-15.08.2/work/kdepimlibs-15.08.2_build/akonadi/src/core/moc_job.cpp:105
#24 0x00007fa5ed79090a in QObject::event (this=0x22e6b00, e=<optimized out>) at kernel/qobject.cpp:1239
#25 0x00007fa5ee077d0c in QApplicationPrivate::notify_helper (this=this@entry=0x2000ce0, receiver=receiver@entry=0x22e6b00, e=e@entry=0x22f3520) at kernel/qapplication.cpp:3716
#26 0x00007fa5ee07d418 in QApplication::notify (this=0x7ffc46412270, receiver=0x22e6b00, e=0x22f3520) at kernel/qapplication.cpp:3499
#27 0x00007fa5ed7662ac in QCoreApplication::notifyInternal (this=0x7ffc46412270, receiver=0x22e6b00, event=event@entry=0x22f3520) at kernel/qcoreapplication.cpp:965
#28 0x00007fa5ed7691d8 in sendEvent (event=0x22f3520, receiver=<optimized out>) at kernel/qcoreapplication.h:224
#29 QCoreApplicationPrivate::sendPostedEvents (receiver=receiver@entry=0x0, event_type=event_type@entry=0, data=0x1ff7bd0) at kernel/qcoreapplication.cpp:1593
#30 0x00007fa5ed7697ea in QCoreApplication::sendPostedEvents (receiver=receiver@entry=0x0, event_type=event_type@entry=0) at kernel/qcoreapplication.cpp:1451
#31 0x00007fa5ed7b5053 in postEventSourceDispatch (s=0x205f500) at kernel/qeventdispatcher_glib.cpp:271
#32 0x00007fa5e62a4344 in g_main_context_dispatch () from /usr/lib64/libglib-2.0.so.0
#33 0x00007fa5e62a4625 in ?? () from /usr/lib64/libglib-2.0.so.0
#34 0x00007fa5e62a46ec in g_main_context_iteration () from /usr/lib64/libglib-2.0.so.0
#35 0x00007fa5ed7b50d4 in QEventDispatcherGlib::processEvents (this=0x20528a0, flags=...) at kernel/qeventdispatcher_glib.cpp:418
#36 0x00007fa5ed764daa in QEventLoop::exec (this=this@entry=0x7ffc464121e0, flags=..., flags@entry=...) at kernel/qeventloop.cpp:204
#37 0x00007fa5ed76c43c in QCoreApplication::exec () at kernel/qcoreapplication.cpp:1229
#38 0x00007fa5edb106bc in QGuiApplication::exec () at kernel/qguiapplication.cpp:1527
#39 0x00007fa5ee0737a5 in QApplication::exec () at kernel/qapplication.cpp:2976
#40 0x00007fa5f07594b9 in Akonadi::ResourceBase::init (r=r@entry=0x20eef70) at /tmp/portage/kde-apps/kdepimlibs-15.08.2/work/kdepimlibs-15.08.2/akonadi/src/agentbase/resourcebase.cpp:602
#41 0x000000000043e463 in Akonadi::ResourceBase::init<ImapResource> (argc=<optimized out>, argv=<optimized out>) at /usr/include/KF5/AkonadiAgentBase/resourcebase.h:193
#42 0x00007fa5ecc637d0 in __libc_start_main () from /lib64/libc.so.6
#43 0x000000000043e319 in _start ()

Additional Information:
 This IMAP resource points to a dovecot 2.2.18 IMAP server on localhost
It holds my email collection from the last 10+ years.
It had been working fine until QT got upgraded from 5.4.2 to 5.5.1

This crash happens every time I turn my machine on and login into KDE, I've not been able to read mail via this IMAP resource, I deleted it and recreated it, and it crashed often while reading the various mail folders and still fails to read and index some of them.

George you can try to enable all features of kdepim:

KDEPIM_FEATURES="akregator kaddressbook blogilo console kalarm kleopatra kmail knotes kontact korganizer ktnef akonadiconsole"

After I emerged kdepim with that, akonadi did not crash again. Well. I think akonadi crashed because there was no new mail coming and kmail was just waiting reading a folder without succes until I restarted akonadi.

Before that I used 
KDEPIM_FEATURES="akregator kaddressbook kalarm kmail knotes kontact korganizer "

So one or all of "blogilo console kleopatra korganizer" did the trick.

oops.. korganiser was emerged, so blogilo, console, kleopatra, ktnef and akonadiconsole were new.
sorry, I can not change my previous message.

interesting, I don't have blogilo enabled, I'll do so and try again.

ok this week akonadi crashed again.
however 'akonadictl status' returned that akonadi was running.
But in kontact kmail keeps waiting reading a folder and when i restarted akonadi, everything was fine.... for a short while.
So I removed blogilo and kleopatra but that did not change anything.

And then... I emptied the trash folders. One trash folder had about 16,9 Mb of data if I remember right but I don't know how many messages.
And no crash anymore.

Using akonadi 15.08.3 and kmail/kontact 5.0.3

This bug has never been confirmed for a Kontact version that is based on KDE Frameworks, except possibly a Technology Preview version 5.0.x. Those versions differ significantly from the old 4.x series. Therefore, I plan to close it in around two or three months. In the meantime, it is set to WAITINGFORINFO to give reporters the opportunity to check if it is still valid. As soon as someone confirms it for a recent version (at least 5.1, ideally even more recent), I'll gladly reopen it.

Please understand that we lack the manpower to triage bugs reported for versions almost two years beyond their end of life.

Just as announced in my last comment, I close this bug. If you encounter it again in a recent version (at least 5.1 aka 15.12; preferably much more recent), please open a new one unless it already exists. Thank you for all your input.