Windows Mail is not compatible with most McAfee or
Norton security programs. Those will need to be
uninstalled, not just disabled.
After uninstalling your non-compatible antivirus, test
your email sending. If it still does not work, the account
has been corrupted by Norton. Delete the account, restart
Windows Mail, then recreate that account.
At your convenience, download and install a more compatible
antivirus like the free Avast:
http://www.avast.com/eng/avast_4_home.html
Even compatible antivirus programs will need to have their
email scanning option turned off. For more on this topic see
http://www.oehelp.com/OETips.aspx#3
Gary VanderMolen