As an interim fix, try this: delete your email account, restart
Windows Mail, then recreate that account. If that fixes the
problem, it means your antivirus was corrupting the email account.
Email scanning in any antivirus must be disabled. For more on this,
see http://thundercloud.net/infoave/tutorials/email-scanning/index.htm
After running Vista 64 and Windows Mail for months with no trouble, I also
have this exact same problem as of today. I am using no other antivirus
software. It is extremely annoying to have to log in every time I open
Windows Mail. Was this caused by an automatic Vista "update"? There must be
a way around this. Stop the insanity.
It isn't clear to me what "no other antivirus software" means.
No antivirus whatsoever? Any other third party security software
like anti-spyware or firewall?
Try this: delete the account, restart Windows Mail, then recreate
that account.