So, "Use Default Server" does not work anymore on any account. I fixed a couple accounts by just using their own smpte entry and then assigning a password when prompted. My problem now is that I have three accounts that have no option available in TB to change their smpte settings (there is no smpte TB entry at all for them and, again, "Use Default Server" doesn't work anymore. Should I try to figure out how to add this line to an existing account or am I on the wrong track here?

- click 'account settings' - scroll down left side to 'outgoing servers (SMTP) and click there - on this pane, you can create new SMTP servers. be sure that the DESCRIPTION field is unique. you will need that when connecting to an account. - now, click an account within the 'account settings' pane that needs a server and at bottom of the accont pane is a link to the assigned SMTP server. That is a dropdown menu and click the one with the right description.

Thank you, david! I thought that's what I needed but couldn't find the right button to click -- and no wonder -- it was at the top of the page in plain sight.  :)

I'm up and running again on all computers but am curious how that could have happened on all three computers (two of which did not have TB running when I got the power outage. Roadrunner assured me by phone that they haven't recently changed their login policies and so the only other thing I can think of is that TB just now updated to a version that will no longer support the concept of a <Default> SMPTE server. That would not explain, however, why this help board is not flooded with similar complaints. Would appreciate your thoughts just to satisfy my curiosity. Thanks again.

What you experienced is a common problem here, usually because the user consciously did that and, later, the email provider began to enforce the security issue. This is happening because email providers are increasing security by demanding that users of their servers be customers and the SMTP authentication does that. In your case, I wonder if you found several SMTP servers already there on that screen. DId you? Or was there just one when you added the others? My 'guess' is that thunderbird allocated the right SMTP server but, since there was no name in description field, when you reactivated thunderbird, things went kerflooey (pardon the technical term...) This is enforced by the email host, not thunderbird. Anyway, I'm glad all is well.