Some transactional emails, including password reset emails, get rejected by the receiving server. E.g. you have an email address @mac.com or outlook.com and that server is rejecting the password reset email, so you’re never seeing it. When we verify that is happening, we can put an exception into our system to tell it to send via a different outbound server, when it sees an email address with that domain, and see if that resolves the issue for the receiving server. We’ve done that now for a number of email providers.