Unable to send mail in Plesk with Postfix: status=deferred (Host or domain name not found. Name service error for name=example.com type=MX: Host not found, try again)

Symptoms

• Postfix cannot send emails leaving the messages in queue.

• RHEL/CentOS/CloudLinux is installed on the server.

• The following entries can be found in /var/log/audit/audit.log:

  PLESK_INFO: type=AVC msg=audit(1375899192.013:10985): avc: denied { read } for pid=2769 comm=”tcp-env” name=”resolv.conf” dev=sda1 ino=1892366 scontext=unconfined_u:system_r:sendmail_t:s0-s0:c0.c1023 tcontext=system_u:object_r:httpd_sys_content_t:s0 tclass=file

  ---

  PLESK_INFO: type=AVC msg=audit(1528811014.613:26279): avc: denied { read } for pid=512 comm=”smtp” name=”resolv.conf” dev=”dm-0″ ino=392479 scontext=system_u:system_r:postfix_smtp_t:s0 tcontext=system_u:object_r:httpd_sys_content_t:s0 tclass=file

• The SELinux context on /etc/resolv.conf file looks as follows:

  # ll -Z /etc/resolv.conf
  -rw-r–r–. root root system_u:object_r:httpd_sys_content_t:s0 /etc/resolv.conf

• Following entries can be found in /var/log/maillog:

  PLESK_INFO: postfix/smtp[25846]: D615A60A1CE: to=[email protected], relay=none, delay=0.15, delays=0.15/0/0/0, dsn=4.4.3, status=deferred (Host or domain name not found. Name service error for name=example.com type=MX: Host not found, try again)

Cause

SELinux is blocking access to /etc/resolv.conf and therefore the mail server cannot resolve destination where the message should be sent.

Resolution

Restore the default context for /etc/resolv.conf file:

1. Connect to the server using SSH

2. Restore the default context on /etc/resolv.conf:

   # restorecon /etc/resolv.conf

Additional information

Mail queue contains deferred emails: Host or domain name not found

RedHat Bugzilla: NetworkManager writing out resolv.conf with wrong context