Hi,this worked for me, (Win Me,Outlook Express, NIS 2003).
Open O/Express > Tools > Options > Connection tab > then Untick 'Hang up after Sending and Receiving'> Apply > OK.
Send yourself a test email.
Oh by the way, check that O/Expr (if you are using that) is configured in the Program Control of Norton.
Open NIS > Personal Firewall > Configure > Program Control.
Hope this is of some help.