Sequoia all Mail smart boxes disappeared yesterday

My guess would be messages with Attachments. If you ctrl-click it you can edit the mailbox. That might give a clue as to its purpose.

All Mail should be in Favorites, not Smart Mailboxes.

If you have a Favorites header, but nothing below, hover over the right side of the header and click the disclosure triangle.

Tony Rees wrote:

Sequoia all Mail smart boxes disappeared yesterday. Did restart etc etc no they are gone. There is one mailbox labeled “attach” which when opened I think has some, of the smart mailbox data

Is this a matter of moving your mouse to the right side to reveal the options—and spin the caret open...(?)

Tony Rees wrote:

Thanks for that. Yes it does contain attachments after 1/1/23 though "who" created it I have no idea. As I said I had several smart mailboxes, but they have all gone and only this smart box for attachments has been created in its place???? Go figure!

I think I picked up on that, but was stuck on "All Mail" which is not what you meant.

I don't know what to do to try to recover them.

Do you have that email account on multiple devices?

This has happened to me too. All I have now is one called "Today". All of the ones I created are done. I've checked that all updates have been applied. I've rebooted. They are gone - which is more than an inconvenience to rebuild. They were very important.