Start *Windows'* safe mode with networking enabled - win10 http://windows.microsoft.com/en-us/windows-10/change-startup-settings-in-windows-10 Still In Windows safe mode, start thunderbird in safe mode - http://support.mozillamessaging.com/en-US/kb/safe-mode

Does problem go away?

bassman212 said

I have 5 mailboxes that I use with Thunderbird. I am using Windows 10. All settings are set the same way on each mailbox and are coming off of the same server. Four of the mailboxes work perfectly but one will lock up Thunderbird if I mark an email as spam. By closing and reopening Thunderbird, It operates OK till I mark an email as spam on the same maibox. Forgive me if I posted this in the wrong place but I have looked for sometime to let you know of a possible problem.

This worked while I was in safe mode. I will let you know if it doesn't work after I re-boot and receive more mail. Thanks

bassman212 said

This worked while I was in safe mode. I will let you know if it doesn't work after I re-boot and receive more mail. Thanks

If that helped, then your problem was likely antivirus software.

What did you determine to be the cause of your problem?