are you using the all or unified view of folders?

Selecting all folders view, right click the affected folder and select properties and then the repair button.

What does that panel show as size on disk?

Thank you for your reply, I have no idea. I read about this "all or unified" in other posts in an attempt to resolve this trying to find out but did not know where to look for "all or unified. I also did the repair button on the Inbox folder and that did nothing. On your last question, Where do I find "size on disk"?

Sometimes a folder with no unread mail appears empty because the Unread or some other button on the Quick Filter Bar is depressed. The QFB is shown under View/Toolbars; press Alt if the Menu Bar is hidden. Also, does the Status Bar (under View/Toolbars) indicate a number for the Total messages in the Inbox?

Size on disk is shown when you right-click a folder, Properties.

I am running on Linux. I do not have View/Toolbars. Or at least I cannot find it.

Quick Filter shows nothing. See screenshot.

Size on Disk. See screenshot.

I found Unified and All settings. Under both it shows nothing. But I have all my sent mail, drafts and templates.

Is there any device that has or had the account set up as POP, which usually means messages are deleted from the server after download to that device? Is the Inbox empty when you access it through webmail?

Good question. I had a Hotmail account setup in my older laptop. I am reducing the use of MS products and setup Thunderbird on the newer laptops w/o the Hotmail POP. After setting up(TB) I got all my sent mail, my drafts, even my undeleted trash mail but nothing in INBOX. When I use Webmail I get everything. Puzzled in Peru