Rarely, Mac users encounter an “Import Failed” error message when trying to open the Mail app in Mac OS, with a brief Message Import splash screen. The import failure prevents the Mail app from opening any further, and therefore renders the Mail app and inboxes unusable. This can happen on any version of Mail for Mac, sometimes at random, or sometimes after updating system software, if user accounts have been migrated, or in many other situations, including if the Mac hard drive is too full without available disk space.

The full error is usually encountered…