"Microsoft Outlook or Outlook Express sends duplicate emails when
Norton AntiVirus email scanning is enabled
Norton AntiVirus 2002 or 2003 (NAV) is installed and Email Scanning is
enabled. When you enable the Automatic Send feature within Microsoft
Outlook 2002 or Outlook Express 5.0/6.0 and send email, duplicate
emails are sent."
you can either disable the automatic send feature
within Microsoft Outlook/Outlook Express, or you can disable the
Outgoing email scanning feature of NAV email scanning.