Thanks for the quick response.
Nothing changed since I last was able to send mail. One machine has XP firewall, the other has Vista 64 bit firewall. Both have Avast Free plus Spyware Doctor running. No spam killer applications. Disabling the Avast shields allows outgoing mail, enabling them prevents the server connection.
Update: Spyware Doctor is also unable to connect to the server when Avast is up.