I am not quite sure if this is portable issue only, but following I realized:
when I delete let say all messages from the sent folder, all from the inbox etc from the TB GUI, then they do not appear in the TB any more, but the space on the disk (stick) is not freed by that. Checking the folders on the stick, it seems that for every folder in the TB there are somehow two files but nothing is deleted or the files do not go any smaller when items are deleted from the GUI.
Is this so supposed to work? And how do I free the disk space occupied by those files which in fact I do not see any more in the TB itself?
Which of those files can be deleted by hand safely?
To permanently delete them, go to the File Menu, and choose Compact Folders.
It is relatively time consuming, so it doesn't happen automatically when you delete a single email - it also cuts down on writes to disk to do it this way, which makes a big difference to both performance and lifespan on a USB drive.
Hope that helps
See Recommended Additional Settings:
https://portableapps.com/support/thunderbird_portable#recommended
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