Can't delete emails from Inbox

Cannot delete emails on one of two accounts. Highlight the emails I want to delete, hit the delete menu item, and the highlighted emails flash momentarily, my highlight moves to the next non-deleted email - then the emails I am trying to delete reappear. Have tried deleting single emails, multiple; even deleting the entire day, and no luck. “Deleted” items are still there, and the contents are still visible.

I do have an error: [IMAP]NO APPEND failed on the account that cannot be deleted.

You may want to try:

Run an eMC Backup. Remove the account causing the error and re-add it back.