Is there a guarantee the emails will actually send after the fix?

Yes. We don’t call it fixed until we’ve sent a successful test transactional email, watched a real order trigger its confirmation, drained any backlog in the queue, and verified a clean 250 OK at the relay plus SPF/DKIM/DMARC passing at the inbox. If the same bug comes back within the coverage window, we fix it at no extra charge. You also get a short written note on what broke and how to keep email healthy.