Hey there! It sounds like you're dealing with Thunderbird not fully closing sometimes, right? That can definitely be frustrating. Here's what you can try: First, make sure all your add-ons are up-to-date. Sometimes an outdated add-on can cause this. Also, try starting Thunderbird in Safe Mode (you can do this by holding down the Shift key while starting Thunderbird) to see if the issue still happens. If it doesn't, it might be related to an add-on. Lastly, you could try creating a new Thunderbird profile to see if the problem persists there. Give these a shot.

Do you have account settings to empty trash or expunge inbox on shutdown?