Do you know how to use the online interface to your email? Most providers of
email services (such as your ISP) have an online interface to your email.
You can go into there and delete the messages that you have already
received. Hopefully the seventh message is the one that is a problem. You
can try looking at the message there and then delete it, or just delete it.
Windows Mail should not have that problem, but there might be something
wrong with the message. Windows Mail should not get stuck but since it does,
try to get rid of the message causing the problem.
The problem might be caused by your antivirus software. If the problem
occurs again later, then consider the possibility that it is your antivirus
software. The experts that help here will advise you to turn off email
scanning by your AV software if it is on.