claws-mail crashes quite frequently when there are some networking issues like temporary lack of internet connection (at the router -- local host thinks it's online all the time).

Program received signal SIGSEGV, Segmentation fault.
0x00000033c4e325bc in g_type_check_instance_is_a (
    type_instance=type_instance@entry=0x12f7ec0, iface_type=<optimized out>)
    at gtype.c:3975
3975	  check = node && node->is_instantiatable && iface && type_node_conforms_to_U (node, iface, TRUE, FALSE);
(gdb) bt
#0  0x00000033c4e325bc in g_type_check_instance_is_a (
    type_instance=type_instance@entry=0x12f7ec0, iface_type=<optimized out>)
    at gtype.c:3975
#1  0x0000003648fd3066 in IA__gtk_style_detach (style=0x12f7ec0)
    at gtkstyle.c:805
#2  0x000000000060ce7d in gtk_cmctree_node_set_row_style (
    ctree=ctree@entry=0xc965f0, node=node@entry=0x12f7940, 
    style=style@entry=0x0) at gtkcmctree.c:4393
#3  0x0000000000559716 in summary_set_row_marks (summaryview=0xee72a0, 
    row=0x12f7940) at summaryview.c:3957
#4  0x000000000055fad7 in msginfo_mark_as_read (summaryview=0xee72a0, 
    msginfo=<optimized out>, row=0x12f7940) at summaryview.c:3534
#5  0x000000000055fb93 in msginfo_mark_as_read_timeout (data=0x19f30f0, 
    data@entry=<error reading variable: value has been optimized out>)
    at summaryview.c:3551
#6  0x00000033c3e49e43 in g_timeout_dispatch (source=source@entry=0x1a12f60, 
    callback=<optimized out>, user_data=<optimized out>) at gmain.c:4451
#7  0x00000033c3e492a6 in g_main_dispatch (context=0xc9f9d0) at gmain.c:3066
#8  g_main_context_dispatch (context=context@entry=0xc9f9d0) at gmain.c:3642
#9  0x00000033c3e49628 in g_main_context_iterate (
    context=context@entry=0xc9f9d0, block=block@entry=1, 
    dispatch=dispatch@entry=1, self=<optimized out>) at gmain.c:3713
#10 0x00000033c3e496dc in g_main_context_iteration (context=0xc9f9d0, 
    context@entry=0x0, may_block=may_block@entry=1) at gmain.c:3774
#11 0x0000003648f45d71 in IA__gtk_main_iteration () at gtkmain.c:1345
#12 0x00000000004b25f5 in inc_pop3_session_do (session=0x1d6bc00) at inc.c:864
#13 inc_start (inc_dialog=inc_dialog@entry=0x14c3b60) at inc.c:635
#14 0x00000000004b3b20 in inc_all_account_mail (mainwin=0xd07810, autocheck=1, 
    notify=0) at inc.c:388
#15 0x00000000004b3c4e in inc_autocheck_func (
    data=<error reading variable: value has been optimized out>) at inc.c:1495
#16 0x00000033c3e49e43 in g_timeout_dispatch (source=source@entry=0x1d55960, 
    callback=<optimized out>, user_data=<optimized out>) at gmain.c:4451
#17 0x00000033c3e492a6 in g_main_dispatch (context=0xc9f9d0) at gmain.c:3066
#18 g_main_context_dispatch (context=context@entry=0xc9f9d0) at gmain.c:3642
#19 0x00000033c3e49628 in g_main_context_iterate (context=0xc9f9d0, 
    block=block@entry=1, dispatch=dispatch@entry=1, self=<optimized out>)
    at gmain.c:3713
#20 0x00000033c3e49a3a in g_main_loop_run (loop=0xbcd780) at gmain.c:3907
#21 0x0000003648f45b57 in IA__gtk_main () at gtkmain.c:1257
#22 0x0000000000449420 in main (argc=1, argv=0x7fffffffe088) at main.c:1559

That was thread #1, other follow:

Thread 5 (Thread 0x7fffddc74700 (LWP 1854)):
#0  pthread_cond_wait@@GLIBC_2.3.2 () at ../nptl/sysdeps/unix/sysv/linux/x86_64/pthread_cond_wait.S:185
#1  0x0000003001036023 in mailsem_internal_wait (s=0xc42750) at mailsem.c:131
#2  0x00000030010361a8 in mailsem_down (sem=<optimized out>) at mailsem.c:279
#3  0x00000000005ec150 in thread_run (data=0xc4caa0) at etpan-thread-manager.c:331
#4  0x00000033c1a07ee5 in start_thread (arg=0x7fffddc74700) at pthread_create.c:309
#5  0x00000033c16f4b8d in clone () at ../sysdeps/unix/sysv/linux/x86_64/clone.S:111

Thread 3 (Thread 0x7fffef8ce700 (LWP 1846)):
#0  0x00000033c16ea71d in poll () at ../sysdeps/unix/syscall-template.S:81
#1  0x00000033c3e495b4 in g_main_context_poll (priority=2147483647, n_fds=2, fds=0x7fffe00008c0, timeout=-1, context=0xf9af00) at gmain.c:4007
#2  g_main_context_iterate (context=context@entry=0xf9af00, block=block@entry=1, dispatch=dispatch@entry=1, self=<optimized out>) at gmain.c:3708
#3  0x00000033c3e496dc in g_main_context_iteration (context=0xf9af00, may_block=may_block@entry=1) at gmain.c:3774
#4  0x00000033c3e49729 in glib_worker_main (data=<optimized out>) at gmain.c:5473
#5  0x00000033c3e6ea45 in g_thread_proxy (data=0x7fffe8003e30) at gthread.c:798
#6  0x00000033c1a07ee5 in start_thread (arg=0x7fffef8ce700) at pthread_create.c:309
#7  0x00000033c16f4b8d in clone () at ../sysdeps/unix/sysv/linux/x86_64/clone.S:111

Thread 2 (Thread 0x7ffff00cf700 (LWP 1845)):
#0  0x00000033c16ea71d in poll () at ../sysdeps/unix/syscall-template.S:81
#1  0x00000033c3e495b4 in g_main_context_poll (priority=2147483647, n_fds=3, fds=0x7fffe80010c0, timeout=-1, context=0xf929d0) at gmain.c:4007
#2  g_main_context_iterate (context=0xf929d0, block=block@entry=1, dispatch=dispatch@entry=1, self=<optimized out>) at gmain.c:3708
#3  0x00000033c3e49a3a in g_main_loop_run (loop=0xf92960) at gmain.c:3907
#4  0x00000034682d0376 in gdbus_shared_thread_func (user_data=0xf929a0) at gdbusprivate.c:278
#5  0x00000033c3e6ea45 in g_thread_proxy (data=0xe00140) at gthread.c:798
#6  0x00000033c1a07ee5 in start_thread (arg=0x7ffff00cf700) at pthread_create.c:309
#7  0x00000033c16f4b8d in clone () at ../sysdeps/unix/sysv/linux/x86_64/clone.S:111

claws-mail-3.11.1-2.fc20.x86_64