Seen this one MANY times.
Norton AV is acting as an email proxy - It recevies the emails, scans them and sends them on, Or it's supposed to.
What you need to do is to change outlook express so that the email goes to your ISP and not to the AV software.
To do this:
Launch outlook express
Click on tools -> accounts -> Mail
click on your account (there may be more than one in the list)
Click on properties
Click on servers
Change the outgoing mails server from localhost (may be down as 127.0.0.1) to the email server your ISP tells you to use.
Click on OK and test!
If this doesn't work or your not sure let me know.
Gary.