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Postfix mail for domain.com loops back to myself Error and Solution

I can send and receive mail using user@example.com, but system generated emails such as root@mail.example.com bounce backup with an error:

May 1 03:14:52 mail postfix/smtp[62798]: 23CA4BD6B40: to=, relay=none, delay=0.01, delays=0/0/0/0, dsn=5.4.6, status=bounced (mail for mail.example.com loops back to myself)

How do I fix this error?
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Sysadmin because even developers need heroes!!!

What Is The Difference Between Authentication And Authorization?

What is the difference between authentication and authorization? Why it is important to understand difference between the two? Authentication vs. Authorization — what are they and how do they differ?
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Q. I’ve recently changed email user account password using passwd command, for one my postfix email server which requires SMTP authentication before sending an email. Now following error is logged into my /var/log/maillog file:

ERROR: Password not accepted from server: 535 5.7.0 Error: authentication failed: authentication failure

How do I solve this problem under Red Hat enterprise Linux running Postfix with SASL authentication?
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Linux Mail Delivery Failed With DNS Service Unavailable Error and Solution

Q. I get following error message for my postfix email server:

Mail Delivery Failed With DNS Service Unavailable Error and Solution

How do I fix this problem?
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