Problem Sending Email From Outlook 2007

[Gregg]

I've recently upgraded to Office 2007 and when trying to send email via my
Yahoo and Orange POP3 accounts I get a message saying there is an
authentication error connecting to the server.

I can send email fine.

When I click to use secure authentication I get an error from Norton AV
saying my server rejected my connection.

I have removed AV and firewall and tried but to no avail. I reverted back to
Outlook 2003 and it worked fine, but I would like to use 2007.

Any suggestions.