Unable to write the email to the mailbox

[pzbrawl]

Starting this morning, new message titles appear in the inbox but noe can be read. This is the error message:

Unable to write the email to the mailbox. Make sure the file system allows you write privileges, and you have enough disk space to copy the mailbox. Compaction is set to autommatic. Manual compaction makes no diff.

Incomprehensibly, Thunderbird is incapable of distinguishing whether the problem is space or rights. The win10 drive has 400G free. Attempting to access the inbox via File Explorer with administrator rights, though, yields "Access denied".

So, as of this morning, Thunderbird is entirely useless. How do I fix this?

[trolly]

Duplicate, locking. Continue the discussion here: http://forums.mozillazine.org/viewtopic ... &t=2993399