If I remember correctly one of the addons can cause this. Do you have addons installed?

I have: Enigmail 1.8.2 Lightning 4.0.0.1 Provider for Google Calendar 1.0.4

I have disabled them and restarted Thunderbird in safe mode. With the same result.

What happens if you disable Provider for Google Calendar 1.0.4?

Just the same. I have all extensions disabled now.

The only indication I can see is a message "Checking mail server capabilities" in the status bar for a while.

So, what are my options for resolving this?

Is this likely to be fixed in a future version of Thunderbird? Or should go back a version or abandon it?

Is the account that doesn't work a gmail account? What is the server address in tools | account settings?

No, the account is "Microsoft Exchange Server 2003 IMAP4rev1 server version 6.5.7638.1"

The server address is webmail.smltd.com port 993

set network.auth.force-generic-ntlm-v1 true (under Prefernces | Advanced | General | Config Editor)

Does it work?

No, same result.

Sorry for delays.

Assuming your problem is not resolved, hopefully you have reverted by installing 31.7.0. If not you can get it from https://ftp.mozilla.org/pub/mozilla.org/thunderbird/releases/31.7.0/

38.1.0 will hopefully be out next week - we should give that a try.

Thank you, I have reverted to 31.7.0 and the email works fine now.

Now Lightning won't work! That is less of a problem though. Hopefully 38.1 will fix all

You'll need to downgrade Lightning as well. Thunderbird 31 requires Lightning 3.3.3. https://addons.mozilla.org/en-US/thunderbird/addon/lightning/versions/

I have the same problem. After downgrade, the problem is solved. Thank you so much!