Keef's suggests seem to have solved the problem. I was waiting to confirm after I tested things a number of times.
I had the second SMTP account. Either I hadn't clicked the box to add the User Name (same name as on the account), or Tb hadn't asked for my password (same password as on the account).
Anyhow, it now works. That's after a little excitement since "Secure Authentication" got turned on unintentionally. My problem ISP won't accept that.
THANKS, especially to Rev Keef.
seacue