Mail sent via mailx/mail command not delivered at recipient mailbox.

Solution In Progress - Updated -


  • Red Hat Enterprise Linux 7
  • Red Hat Enterprise Linux 8
  • Red Hat Enterprise Linux 9
  • sendmail
  • postfix


  • Email not delivered at recipient mailbox after successfully sending from mailx/mail command.
  • Mail not delivered at destination with error code "554 Blocked" in telnet response..


  • Check the SMTP server's response by connecting to the SMTP server using telnet command.

  • Contact SMTP server vendor to check the ACL or allowed networks if the client system's network is

    enabled or not.

Root Cause

Expected result :

[root@rhel1 ~]# telnet 25
Connected to
Escape character is '^]'.
220 ESMTP mya-m01334238

Actual Result :

[root@rhel2 ~]# telnet 25
Connected to
Escape character is '^]'.
554 Blocked - see
  • If you’ve received a 554 error message, you’ve been blocked from emailing because your email server is not properly identifying itself when connecting to the servers. This identification process is known as Reverse DNS.

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