Mail.app won't search entire messages

I can search by To and From and Subject OK, but searching the body or entire message always turns up nothing.

I have read around for may solutions and tried them all. I've:

• Rebuilding the spotlight index manually.
• In mail, going to Mailbox > Rebuild for all mailboxes.
• Deleting ~/Library/Mail and ~/Library/MailDownloads.
• Deleting all my accounts, iCloud, Gmail, etc.
• Rebuilding the Spotlight index manually again.
• Adding the accounts again.
• Creating a new user and adding a mail account to it. No joy. Can't search.
• Also deleted mail.app and restored it from a version a few months ago.
• EDIT: Also tried deleting Mail using CleanMyMac and then restarting and restoring Mail.app from my most distant Time Machine backup. No joy.

Any other ideas? Start over from scratch?

Will an app like Sparrow have the same problem?