Bugzilla

Do you wish to compact all local and offline folders to save disk space? This will save about 45,7 GB.
inbox1@example.org - 2018: 5152
inbox1@example.org - Inbox: 10087691! more than the size on disk: 7142272
inbox1@example.org - Sent: 15429
[censored] - Inbox: 46329502464! more than the size on disk: 41099881
inbox2@example.org - Folder 1: 2544923598! more than the size on disk: 21445922
inbox2@example.org - Folder 2: 53336492! more than the size on disk: 200532
inbox2@example.org - Folder 3: 53760610! more than the size on disk: 154879
inbox2@example.org - Folder 4: 12595! more than the size on disk: 0
inbox2@example.org - Drafts: 2474288! more than the size on disk: 0
inbox2@example.org - Sent: 47064029! more than the size on disk: 13031952
inbox2@example.org - Folder 5: 1742057


All folders are selected for offline use (so I suppose this is the default).

> May that reported size represent the size of the folder on server?

My inbox is about 50MB on the IMAP server.

> Can you also check, if those folders have the corresponding file called e.g. Inbox.msf alongside the Inbox file and it is not empty?

They are not empty.

> Once you are on the account, please also see the folder where you use to delete messages, use right click->Properties and see "Size on disk", whether it matches the file size of that folder that you can see via the file manager. The file backing that folder is shown in "Location" field of that same dialog.

All these sizes are way off. Before comacting, Folder 1 is about 8MB on disk, and after compacting, it is about 2MB on disk. But both times it is reported as 20MB on disk inside Thunderbird.