Mac Mail search often stops working when the mailbox index or macOS Spotlight database becomes corrupted. First, quit Apple Mail and restart your Mac, then relaunch Mail and try searching again. If it still fails, rebuild the mailbox: select the affected mailbox, choose Mailbox > Rebuild. Next, ensure Spotlight indexing is enabled for Mail by checking System Settings > Siri & Spotlight and removing Mail from Privacy exclusions if present. You can also force a reindex by dragging your main drive into Privacy and then removing it. Another fix is to reset Mail’s envelope index: quit Mail, go to ~/Library/Mail/V*/MailData and delete Envelope Index files, then reopen Mail so it rebuilds them. Updating macOS can also restore search stability, as Apple Mail relies on system indexing. If problems persist, test in Safe Mode or create a new user profile to isolate corruption issues in Apple Mail. Finally, restart once more and verify search results in Smart Mailboxes and global inbox search for full recovery across all accounts and folders after a reboot cycle.