Version:           3.5.1 (using KDE KDE 3.5.1)
Installed from:    Debian testing/unstable Packages
Compiler:          gcc 4.0.2 
OS:                Linux

I routinely get 10,000+ spam message filtered into my Maildir spam folder. Selecting all the message and shift-delete causes kmail large CPU utilization and can take hours to complete.

Similar operations on the same folder using Thunderbird and mutt take minutes.

I'm running kmail as a kpart in kontact, if that matters. But stand-alone kmail does the same thing.

  PID USER      PR  NI  VIRT  RES  SHR S %CPU %MEM    TIME+  COMMAND
 4775 tanner    25   0  146m  96m  31m R 89.8  9.5  45:24.63 kontact

strace on the pid shows (over 5 min period)
$ strace -p 4775
Process 4775 attached - interrupt to quit
gettimeofday({1142624313, 174935}, NULL) = 0
gettimeofday({1142624313, 181478}, NULL) = 0
gettimeofday({1142624313, 183122}, NULL) = 0
gettimeofday({1142624313, 188823}, NULL) = 0
gettimeofday({1142624313, 189389}, NULL) = 0
gettimeofday({1142624317, 955773}, NULL) = 0
gettimeofday({1142624317, 957834}, NULL) = 0
[snip repeats]

Killing kontact with segfault to get a bt is attached

$ kill -s SIGSEGV 4775
Using host libthread_db library "/lib/tls/libthread_db.so.1".
[Thread debugging using libthread_db enabled]
[New Thread -1241418048 (LWP 4775)]
[New Thread -1279562832 (LWP 4929)]
[New Thread -1271174224 (LWP 4928)]
[New Thread -1262785616 (LWP 4927)]
[New Thread -1254397008 (LWP 4926)]
[KCrash handler]
#5  0xb718d2cc in QListViewItem::itemAbove (this=0x9e37ed0)
    at widgets/qlistview.cpp:3920
#6  0xb56b2fba in KMHeaders::prepareMove (this=0x88af6e8, contentX=0x85, 
    contentY=0xbfafc928)
    at /tmp/buildd/kdepim-3.5.1/build-tree/kdepim-3.5.1/kmail/kmheaders.cpp:1442
#7  0xb56c25be in KMHeaders::msgRemoved (this=0x88af6e8, id=6090, 
    msgId=@0xbfafc974)
    at /tmp/buildd/kdepim-3.5.1/build-tree/kdepim-3.5.1/kmail/kmheaders.cpp:1126
#8  0xb56c38c9 in KMHeaders::qt_invoke (this=0x88af6e8, _id=113, 
    _o=0xbfafc9f0) at kmheaders.moc:301
#9  0xb709c7ff in QObject::activate_signal (this=0x8657a78, clist=0x8a502e8, 
    o=0xbfafc9f0) at kernel/qobject.cpp:2356
#10 0xb56f2c0f in KMFolder::msgRemoved (this=0x8657a78, t0=162674712, 
    t1=@0x9b23818) at kmfolder.moc:254
#11 0xb56f6b9d in KMFolder::qt_emit (this=0x8657a78, _id=9, _o=0xbfafcae0)
    at kmfolder.moc:381
#12 0xb709c7d3 in QObject::activate_signal (this=0x8657bc8, clist=0x8658720, 
    o=0xbfafcae0) at kernel/qobject.cpp:2354
#13 0xb571072f in FolderStorage::msgRemoved (this=0x8657bc8, t0=162674712, 
    t1=@0x9b23818) at folderstorage.moc:320
#14 0xb5712051 in FolderStorage::removeMsg (this=0x8657bc8, idx=6090)
    at /tmp/buildd/kdepim-3.5.1/build-tree/kdepim-3.5.1/kmail/folderstorage.cpp:403
#15 0xb57a2394 in KMFolderImap::removeMsg (this=0x8657bc8, 
    msgList=@0xbfafcc70, quiet=false)
    at /tmp/buildd/kdepim-3.5.1/build-tree/kdepim-3.5.1/kmail/kmfolderimap.cpp:286
#16 0xb56f18c6 in KMFolder::removeMsg (this=0x9b23818, msgList=@0x9b23818, 
    imapQuiet=false)
    at /tmp/buildd/kdepim-3.5.1/build-tree/kdepim-3.5.1/kmail/kmfolder.cpp:407
#17 0xb583a8cd in KMMoveCommand::execute (this=0x9bd4238)
    at /tmp/buildd/kdepim-3.5.1/build-tree/kdepim-3.5.1/kmail/kmcommands.cpp:1965
#18 0xb582cdab in KMCommand::slotPostTransfer (this=0x9bd4238, 
    result=KMCommand::OK)
    at /tmp/buildd/kdepim-3.5.1/build-tree/kdepim-3.5.1/kmail/kmcommands.cpp:255
#19 0xb58333b6 in KMCommand::qt_invoke (this=0x9bd4238, _id=5, _o=0xbfafcdd4)
    at kmcommands.moc:148
#20 0xb58336ab in KMMenuCommand::qt_invoke (this=0x9b23818, _id=162674712, 
    _o=0x9b23818) at kmcommands.moc:2436
#21 0xb5833743 in KMMoveCommand::qt_invoke (this=0x9bd4238, _id=5, 
    _o=0xbfafcdd4) at kmcommands.moc:2619
#22 0xb709c7ff in QObject::activate_signal (this=0x9bd4238, clist=0xa0b1fd8, 
    o=0xbfafcdd4) at kernel/qobject.cpp:2356
#23 0xb582bab2 in KMCommand::messagesTransfered (this=0x9bd4238, 
    t0=KMCommand::OK) at kmcommands.moc:126
#24 0xb5832f1d in KMCommand::transferSelectedMsgs (this=0x9bd4238)
    at /tmp/buildd/kdepim-3.5.1/build-tree/kdepim-3.5.1/kmail/kmcommands.cpp:350
#25 0xb5833187 in KMCommand::slotStart (this=0x9bd4238)
    at /tmp/buildd/kdepim-3.5.1/build-tree/kdepim-3.5.1/kmail/kmcommands.cpp:247
#26 0xb58333c8 in KMCommand::qt_invoke (this=0x9bd4238, _id=4, _o=0xbfafcf58)
    at kmcommands.moc:147
#27 0xb58336ab in KMMenuCommand::qt_invoke (this=0x9b23818, _id=162674712, 
    _o=0x9b23818) at kmcommands.moc:2436
#28 0xb5833743 in KMMoveCommand::qt_invoke (this=0x9bd4238, _id=4, 
    _o=0xbfafcf58) at kmcommands.moc:2619
#29 0xb709c7ff in QObject::activate_signal (this=0x8158c58, clist=0x9cac458, 
    o=0xbfafcf58) at kernel/qobject.cpp:2356
#30 0xb742a421 in QSignal::signal (this=0x8158c58, t0=@0x8158c80)
    at .moc/debug-shared-mt/moc_qsignal.cpp:100
#31 0xb70b9eec in QSignal::activate (this=0x8158c58) at kernel/qsignal.cpp:212
#32 0xb70c19b0 in QSingleShotTimer::event (this=0x8158c30)
    at kernel/qtimer.cpp:286
#33 0xb7033122 in QApplication::internalNotify (this=0xbfafd580, 
    receiver=0x8158c30, e=0xbfafd2c8) at kernel/qapplication.cpp:2635
#34 0xb7033314 in QApplication::notify (this=0xbfafd580, receiver=0x8158c30, 
    e=0xbfafd2c8) at kernel/qapplication.cpp:2358
#35 0xb7736fde in KApplication::notify (this=0xbfafd580, receiver=0x8158c30, 
    event=0xbfafd2c8) at kapplication.cpp:550
#36 0xb6fc4861 in QApplication::sendEvent (receiver=0x8158c30, 
    event=0xbfafd2c8) at qapplication.h:520
#37 0xb7024bad in QEventLoop::activateTimers (this=0x80ba658)
    at kernel/qeventloop_unix.cpp:556
#38 0xb6fd8566 in QEventLoop::processEvents (this=0x80ba658, flags=4)
    at kernel/qeventloop_x11.cpp:389
#39 0xb704bb01 in QEventLoop::enterLoop (this=0x80ba658)
    at kernel/qeventloop.cpp:198
#40 0xb704ba26 in QEventLoop::exec (this=0x80ba658)
    at kernel/qeventloop.cpp:145
#41 0xb7031c35 in QApplication::exec (this=0xbfafd580)
    at kernel/qapplication.cpp:2758
#42 0x0805ae7b in main (argc=162674712, argv=0x9b23818) at main.cpp:177
#43 0xb77fbeb0 in __libc_start_main () from /lib/tls/libc.so.6
#44 0x08058561 in _start () at ../sysdeps/i386/elf/start.S:119

Other potentially related bugs:
Bug: #96651