Sendmail config error: mail loops back to me (MX problem?) solution

Yesterday, I didn’t have this problem. After one night, Sendmail reported this error by sending an internal email. Remember yesterday, it just added SMTP authentication, so it has nothing to do with this loops back.
Add the local domain name in local-host-Names, don’t bring mail, restart the Sendmail service, and everything is fine. Many online solutions require changes to your HOSTS, and I haven’t changed either.

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