I've been noting problems with various webmail systems.
Here are some posts to backup what may be causing some of these problems, as I have noted most of the mail systems I've used are horde or php. These advisories came from Secunia today:
Horde:
http://secunia.com/advisories/28020/
PHP:
http://secunia.com/advisories/28393/
Now...will someone please look into these AJAX systems as well? Something seems a little fishy with some of those.