Messages may be stuck in the Outbox when you use Windows Mail on a computer
that is running Windows Vista
http://support.microsoft.com/kb/941090
It also works on other folders.

Messages may be stuck in the Outbox when you use Windows Mail on a computer
that is running Windows Vista. Applies to other folders as well.
http://support.microsoft.com/kb/941090

Few of the more helpful responders on this newsgroup will respond by email.

For the undeletable message problem, download and install this hotfix, with
Windows Mail not running:

http://support.microsoft.com/default.aspx/kb/941090

Although it's labelled as for mail stuck in the Outbox, it also works in
other folders.

Ron;720733 Wrote:

Hi Ron,

This will help show you how to fix the stuck undeletable email message
problem in Windows Mail for all folders.

Installing the KB941090 update will just fix the problem for now. You
must stop the cause to prevent it from happening again. Read the section
titled "FIRST" in this tutorial about antivirus and other security
programs to help prevent this from happening again, then install the
KB941090 Microsoft Update in the section titled "SECOND" to fix and be
able to delete the stuck message from the problem folder.

'Windows Mail problems'
(http://www.vistax64.com/tutorials/62560-windows-mail-problems.html)

Shawn