Getting messages in sendmail "stat=Deferred: 450 service permits 2 unverifyable sending IPs"

Solution Unverified - Updated -

Issue

  • When sending a mail to test.net it is undelivered with the following message:
 Mar  9 04:05:27 mail sendmail[30406]: s8UX012712: to=<test@test.net>, delay=4+05:48:18, xdelay=00:00:17,     mailer=esmtp, pri=8490891, relay=test-relay.test.net. [xx.xx.xx.xx], dsn=4.0.0, stat=Deferred: 450 service   permits 2 unverifyable sending IPs - mail.domain.com is not xx.xx.xx.xx
  • Why reverse dns is necessary in email setup for public facing ip?

Environment

  • Red Hat Enterprise Linux 4

  • Red Hat Enterprise Linux 5

  • Red Hat Enterprise Linux 6

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