What error message are you seeing in that instance?

"Your message was sent but a copy was not placed in your sent folder (Sent) due to network or file access errors.

You can retry or save the message locally to Local Folders/Sent-gwalchmai@scattercreek.com."

“Retry” – same thing happens as the first time. “Save” – the message disappears and does not appear in my Sent Folder, nor in my Local/Sent folder.

What you're experiencing are problems in the network, as indicated. You can do a workaround by changing your sent folder to use the PC and store locally. I have had that problem and that technique was useful.

"changing your sent folder to use the PC and store locally." Um... how do I do that?

in account settings, click 'copies&folders' and there you can change location of Sent folder.

That worked, Thank you!

However, as of this morning, Thunderbird is not picking up new messages. My email server, scattercreek.com, has roundcube webmail -- same account, just a different door into it. Right now, roundcube shows three new messages that are not showing up in Thunderbird, despite several clicks on "Get Messages." And Thunderbird keeps popping up a little box that says "connection with scattercreek.com has timed out." I checked with scattercreek tech support, and they say all my settings are correct from their end.

I'm baffled.

I've been using Firefox/Thunderbird for at least 20 years, and have loved them both, have even donated a few pennies, on occasion. This most recent update of Thunderbird, however, seems to have a few bugs??

Roundcube is an online email product and uses different connections that Thunderbird. The timeout could be network problems for scattercreek. Something to try would be to do this: - go to settings>general - start the config editor - locate mailnews.tcptimeout and change default from 100 to 300. That may be sufficient for this issue,

Did that, & it still timed out without picking up any of the dozen emails that roundcube shows for today. Sorry.