Solution: Some Mac OS Mail Favourites are grayed out and cannot be deleted

I encountered the issue of a grayed out folder that can’t be deleted, in MacOS Mail app today. The discussion on Apple’s forums does not provide any actionable answers. After a while I figured out a solution myself and it’s very simple:

  1. Create a new mailbox (Mailbox -> New Mailbox…). For Location, choose “On My Mac” and name it the same as the grayed out folder in Favourites that you’re struggling with.
  2. Once you add this new mailbox, the one in Favourites should become accessible again. You can now right click on it and hit “Remove from Favourites”.
  3. You can now also delete the empty local (On My Mac) mailbox folder that you created in step 1.

Hope that helps.