Software

Just as a test and in hope to narrow down problem areas take that system off the firewall see if it works. This will help you in where to troubleshoot firewall, or outlook. Also if you think it is the isp then setup the email account from a system at home or another system off site and see if you still get the outgoing server error.

On off-site computer with the same ISP, operating system and version of outlook, and the same account settings, the connection was established, mail server found, and test message sent.

When the computer that isn't working is off the firewall, the message still occurs.

Most smtp servers require authentication to send mail to prevent spammers from sending unauthorized mail. Check in the account setup and see if the setting on the Server tab has the option checked for Outgoing Mail Server has the checkbox checked where "My server requires authentication" and that the Settings (click on the Settings button) has the "Use same settings as my incoming mail server" is selected.

Cheers.

RW