I recently converted from Outlook to Thunderbird and use a Local Folder to maintain most of my emails. Everything seemed to run well for the first few days, but then I realized most emails being automatically copied by filters are showing up 2 blank messages (same subject/date/time/etc.). I get the occasional 12/31/1969 email as well. Oddly, when I run the filters manually, the process works flawlessly and have never resulted in duplicated blank messages or a 1969 email. '''Any opinions on why an automatically-ran filter corrupts most emails but manual runs are fine?''' The behavior is bad enough I'm considering switching back to Outlook. This is such a basic function it causes me doubt in Thunderbird's ability to safely manage my emails. Notes: - Using Proton Mail Bridge - Latest Thunderbird/latest Proton Mail Bridge with no add-ons or extensions - Repairing or compacting the associated Local Folder doesn't fix any message. The only 'fix' is to manually re-copy the affected message from my server, then delete the corrupt copies. - The filters are set to run with new email - Each filter copies the message to the Local Folder, then moves the message to the server's Trash. This two-step action is because Proton Mail Bridge does not allow third-party clients to move messages out of the server--if you do this, it orphans the email in their All Mail folder and become a mess to clean up. - After extensive research, I thought my folders were corrupt so I completely rebuilt the Local Folder structure. All messages were moved into new folders and the original folders were deleted. - Each folder is a few hundred MB, total Local Folder size is less than 7GB