Horhe said

When emails sent directly through WindStream, a copy is saved in the WS folder for SENT MAIL. When emails sent using ThunderBird (going through WS as the ISP), no copy is saved. How to fix this and get copy in TB folder??? Help, please.

Added Info: Maybe this will help diagnose the issue above. TB also shows an error msg that WS does not recognize the command ID. Possibly TB commands no longer match WS requirements?? Help, please.

There have been several reports of issues with windstream. The message you get is from the server and is likely to have nothing to do with Thunderbird. Apparently windstream are in the process of migrating their servers. This might be causing you the problem. Read the comments at the following link and you will discover you are not alone. http://downdetector.com/status/windstream