I have a smart mailbox in Apple Mail, which includes messages that are unread and which aren’t in any of half a dozen “proper” mailboxes. It’s worked nicely for some time.
Under Mail in High Sierra on my iMac (2013), however, four messages have become stuck in this smart mailbox. They have been read; they are not “unread”, in that they do not appear in bold; but they don’t disappear from the mailbox. I can choose another mailbox and return; I can quit mail and start again; but they are still there.
They sometimes appear in the “unread count” next to the mailbox name, and sometimes not. If I mark them as unread, then as read again, they will disappear from the count but they’ll still be in the list when I select the mailbox. If I quit Mail, they feature again in the count.
I’ve tried re-syncing the accounts (my Mail has three mail accounts: two of the messages are in one account and two in another). I’ve restarted the Mac. I’ve told Spotlight to ignore the whole disk and then to re-index it, in the hope that that might have something to do with it. I’ve deleted the smart mailbox and re-created it from scratch.
No dice. The damn things are still there. They have various different dates; other messages received on those days and read do not appear.
In Mail under Sierra on my MacBook Pro, there’s no such problem. The unread messages show up; the read ones don’t.
I’ve run out of things to try. Any ideas gratefully received.