Claws just breaks with a bug report:

Claws Mail version 3.7.9
GTK+ version 2.24.5 / GLib 2.29.10
Locale: en_US.UTF-8 (charset: UTF-8)
Features: IPv6 iconv compface GnuTLS LDAP JPilot GNU/aspell libetpan libSM
Operating system: Linux 2.6.38.8-desktop-5.mga2 (x86_64)
C Library: GNU libc 2.12.1
--
[Thread debugging using libthread_db enabled]
0x00007fb4b812de3e in waitpid () from /lib64/libpthread.so.0
#0  0x00007fb4b812de3e in waitpid () from /lib64/libpthread.so.0
No symbol table info available.
#1  0x000000000049572b in ?? ()
No symbol table info available.
#2  <signal handler called>
No symbol table info available.
#3  0x00007fb4b39845e7 in XGetXCBConnection () from /usr/lib64/libX11-xcb.so.1
No symbol table info available.
#4  0x00007fb4b94ac511 in sn_display_new ()
   from /usr/lib64/libstartup-notification-1.so.0
No symbol table info available.
#5  0x00000000004f101a in ?? ()
No symbol table info available.
#6  0x00000000004f4b14 in main ()
No symbol table info available.
Kill the program being debugged? (y or n) [answered Y; input not from terminal]

It has been reported and solved upstream, but in CVS:

http://www.thewildbeast.co.uk/claws-mail/bugzilla/show_bug.cgi?id=2414