Smart Mailbox no longer working

The Smart Mailbox I have set up for Wells Fargo emails has stopped populating since January 2016. Previously it had populated properly since I made it in 2010.

I have since received many Wells Fargo Bill Pay emails - but they don't populate into the Smart Mailbox.

I have created another Smart Mailbox with the same name but with a number one (1) after. It shows exactly the same emails.

Solution 1:

What fixed it for me was this procedure, i.e.:

1. Go to the Applications > Utilities folder.
2. Open Activity Monitor.
3. Select “All Processes” from the View menu.
4. Search for “mds”.
5. Select and quit each instance of “mds” and/or “mdserver” separately (force-quit if you have to).

I had only one instance of “mds”. Force-quitting it was enough to instantly solve the problem. Kudos to MacIssues!