Norton antivirus is among the top three troublemakers for Windows Mail.
Symptoms often don't start until months later.
The only way you can prove or disprove that Norton is the culprit is to
uninstall it, followed by using their debris removal tool: http://service1.symantec.com/Support/tsgeninfo.nsf/docid/2005033108162039
Another option is to upgrade to Windows Live Mail, which is more
resistant to the adverse effects of aggressive antivirus products: http://get.live.com/wlmail/overview
