Have you tried restarting your computer? The first the to do when there are issues. I really do not have any idea what deleting the global message index would do to getting mail. https://support.mozilla.org/en-US/kb/rebuilding-global-database I do not doubt there are a very few limited circumstances where that might help. If Thunderbird was stuck on determining what messages to index in the activity manager. But as a general fix all, I think it would be overkill as few folk with issues will be able to get value from doing so. A really good starting point is what error messages are you seeing? Or in the absence of an specific error message, what is shown on the status bar at the bottom that leads you to think it is stuck? The vast majority of issues in retrieving mail on Windows machines and any others with anti virus programs are those anti virus programs. This is especially so if they use self signed certificates to hack you encrypted communications (most of them). If they have a firewall component they are rather fond of blocking new versions of Thunderbird post update. It is for this reason we suggest initially restarting Thunderbird in troubleshoot mode from the help menu and continuing when prompted to see if that improves the situation. Sometimes it is an addon and safe/troubleshooting mode blocks those. The next step is to restart the device in [https://support.microsoft.com/en-us/windows/start-your-pc-in-safe-mode-in-windows-92c27cff-db89-8644-1ce4-b3e5e56fe234 safe mode with networking]. This starts windows in a limited mode that blocks startup programs and some enhanced features. But if Thunderbird works correctly in that mode, there is not an issue with thunderbird, but with a startup program.