Try right clicking the folder and selecting compact. Just to see if you get another answer. Right click the folder that is giving the message, select properties... what is the size on disk?

Thank you Matt. If I select only one folder and run compacting it is the same message. I have 98 GB of free space. If I set the "properties" of a folder, I have information as in the attachment jpg. I notice that it is shown to be 154 GB but I am convinced that this is not true. My synchronization with the server is only for 2 weeks.

Hi, do you have any more ideas?

is your account IMAP by any chance?

Yes, IMAP

then with Thunderbird simply closed (not running in the background) delete the file and the MSF and mail will be redownloaded from the mail server when Thunderbird restarts. Normally I would suggest you rename them, and wait until things settled with the new mail download before deleting, but if the mail you have on the server exceeds the 60Gb you have free then things will get incalculably worse. Do you have any idea how much space you mail occupies on the server? Perhaps check that first. I am exceedingly nervous about telling someone to just delete it without a way to go back it I get it wrong.

Hi. So far it has fixed itself, I don't know what happened, but it started working. If the problem returns, I will try your tips. Thanks Matt.