All was well with Thunderbird until Windows crashed about 2-months ago. Took it to a repair shop and had it fixed, including a re-install of Windows 10 Home Edition. Reloaded Thunderbird and noticed it was very sluggish sending emails and transferring them to the "Sent" folder. Also getting messages saying email could not be copied to "Sent" folder and/or email was not sent (even though it WAS sent and in the sent folder). Also very slow to move emails to from "Inbox" to "Trash" or other Thunderbird folders. Thought my AVG anti-virus was causing the problem so I dumped it and installed Avira. Problems did not go away. Did a thorough un-install of Thunderbird using Revo and re-installed, then transferred the address book and email files into the newly installed program (did NOT use any of the old profile files). Still got the same problems! Another question - why is there a "Sent" main folder and a "Sent Mail" sub-folder in the "Trash" main folder? So may questions, so few answers! Bob