I am missing my "all mailboxes" in my menu box

I take it that you mean "All Inboxes", and not "All Mailboxes".

Two possibilities:

a) This is already there, but hidden. In this case, hover the cursor near the word "Favorites", and click the disclosure triangle to show all the Favorites

b) The disclosure triangle for "Favorites" is twirled open, but "All Inboxes" are not there. In this case, press the circled + sign and select All Inboxes to add them to the list.

When you do a search, you can still search all mailboxes.

Frankly, I do not see a point in having an "All Mailboxes" under Favorites. By selecting this I would have tens of thousands of e-mails in a single window.

Just enter a search by clicking the magnifying glass, an "All Mailboxes" appears under Search at the top of the Sidebar:

(please ignore)

No, I still have "all inboxes", I used to also have "all mailboxes" too but it's gone now. Using search in "all mailboxes searches all your inboxes and also all of the mailboxes you created. I've tried your suggestions but they didn't work unfortunately. But thank you

What was the solution please? It doesn't seem to be showing. I have the same issue with "all mailboxes' missing.

Thanks

Thank you