"Ange" ...
> Since 21st August, I have been unable to send e-mails although I can
> receive
> them without a problem. I had a similar problem in March when Microsoft
> advised me to restore my system to a date prior to a recent update. This
> worked and up until 21st August there have been no problems. My husband
> has
> exactly the same outgoing mail set-up and can send e-mails without a
> problem.
> I have restored my system to 17th August but still no joy. There is an
> e-mail in my outbox that I cannot delete which I suspect is causing the
> problem. Any advice?

You are most likely a victim of incompatible antivirus software.

Use this utility http://www.oehelp.com/WMUtil/Default.aspx
to remove the message stuck in your outbox.
Follow all the instructions for the required functionality to be
available.

If you are a victim of Norton or McAfee...

Get rid of the incompatible AV software, uninstall entirely,
and use a free compatible alternative such as Avast
http://www.avast.com/eng/avast_4_home.html

Disable email scanning or better yet omit it during the install
processes http://www.oehelp.com/OETips.aspx#3

At this point you should delete and recreate your email
account within Windows Mail to remove corruptions.

Next, use this utility http://www.oehelp.com/WMUtil/Default.aspx
to remove the message stuck in your outbox.
Unfortunately, you've a poor track record, you'll have to read and
follow all the instructions for the required functionality to be
available.