one of the accounts stopped working.

You'd certainly need to be more specific about your problem.

I apologize, I shouldn't have assumed that was straightforward - it could mean a number of things.

By "stopped working" I mean that I could not connect to that specific mail server with Thunderbird. Everything stored locally was fine, but it would time out when trying to receive new messages.

Are there any more specifics I should provide?

See if this article helps. https://support.mozilla.org/en-US/kb/cannot-receive-messages

Thanks for the quick reply christ1,

I triple-checked the server settings, which work fine in TB 37, and tested a dozen variations in TB 38. I removed all associated passwords under security, and have tried this over several different Internet connections. It is definitely something different related to TB 38...

Can you check whether there's anything suspicious in the error console? Tools (Alt-T) - Error Console

Great idea, didn't realize Thunderbird had an error console right there in the menu! The following error comes up:

Error: An error occurred during a connection to (SERVER NAME). SSL received a weak ephemeral Diffie-Hellman key in Server Key Exchange handshake message. (Error code: ssl_error_weak_server_ephemeral_dh_key)

Greek to me :)

christ1, I've looked further into the error and noticed that you responded to a number of similar issues. Guessing now that this is related to increased security in TB related to the logjam attack earlier this year. Perhaps our company server needs a security update.

Any of this sound right? Thanks again for your time and help.

Guessing now that this is related to increased security in TB related to the logjam attack earlier this year. Perhaps our company server needs a security update.

You hit the nail on the head. See https://support.mozilla.org/en-US/questions/1072942#answer-755678

Thanks again!