Thunderbird 38.3.0
I use "Shift-Delete" on a regular basis to keep selected EMAILs from residing in TRASH.
Again today, I hit "Shift-Delete" to erase a single email, and everyone of my InBox emails was erased.
I then went to Trash, clicked on a single email to move to back and all emails in Trash were automatically erased. I then shut down the system and rebooted.
I've had this occur about 6 times. The last time I posted this problem it was suggested to compact emails.
I now compact whenever prompted. I also move almost all my emails to local folders so they do NOT build up in the InBox.
Don't know if I'm holding the Shift-Delete keys to long and multiple messages are being generated,
but appears to be a BUG as # of emails have varied from <20 to over 80 when this has occurred.
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One nice addition would be the ability to confirm where emails end up. I personally get tired of deleting
the same Emails from InBox, Trash, and Sent,