The message seems to have gone away after I did a File: Compact Folders command. In years of use, we had never done a Compact Folders command. We recovered gigabytes of space.

This message still is a problem, but no longer for us. Unfortunately it has not effect on our original problem (failure of pop3 mail pickup).

The message is not useful to a user. It should be couched it terms that a user can deal with. My *guess* is that some size has become too big to fit in a 32-bit integer (signed or unsigned?). Does that have any effect on the user or the operation of the program?

Fair question: why would a user see this? It appears on the Error Console and, on Linux, on the terminal if you invoked Thunderbird from the terminal (standard out or standard error). I saw the message and was confused by it when I was trying to debug other misbehaviour.

You are looking in the error console. Which is accessed via the developer menu. Perhaps you need to reconsider what it should display as the developer will be interested in the code error. Not some sanitized version of what occurred that has been translated into whatever language is in use, by someone that at times has used their own version of Chinese whispers in the process.

So perhaps we can look at the actual problem. You are not getting mail. Not at all uncommon for windows users with a third party antivirus program installed post an update.

Generally we recommend starting Thunderbird in Troubleshoot mode (it is on the help menu) as that gets rid of addons themes and other injected code from third party programs.

If that is unsuccessful restart the operating system in safe mode with networking and try running Thunderbird in this special mode of the operating system. Often this will see tings start up because the third party software is not loaded in safe mode.

Finally you could log the connection. But I would not recommend that as you are apparently seeing no error messages, or perhaps after enough time a time out. Classic signs of a software firewall blocking access.

Matt: thanks for your help

You are right that it is on the error console (and terminal). But perhaps something should be shown to the user.

When I googled for this message, I got a number of hits. So others are getting it. Interestingly, none of the hits actually were about the error, it just showed up in posted logs.

If the message doesn't matter, consider getting rid of it. If the message matters, it should trigger some kind of signal to the user.

Also: Is there any mechanism to prompt the user to do a "Compact Folders" command when it would be a Good Idea? I know that it is rarely urgent.

This was an old Ubuntu system, not Windows. The actual problem is unknown but it was solved by updating the self-signed x509 certificate on the POP3 server and then re-importing it (the old one was going to expire in a few days anyway). I reported in another query. In general, problems with TLS authentication are barely reported and non-specific.

FWIW this is also reportedin https://bugzilla.mozilla.org/show_bug.cgi?id=1788200