Why Sendmail service failing to start in RHEL 7?

Issue

• Sendmail service does not start.
• Service sendmail fails to create socket.
• Sendmail service status shows problem in creating SMTP socket.

 mail]# systemctl status sendmail
● sendmail.service - Sendmail Mail Transport Agent
   Loaded: loaded (/usr/lib/systemd/system/sendmail.service; enabled; vendor preset: disabled)
   Active: active (running) since Wed 2015-12-30 17:34:59 EST; 4s ago
  ExecStart=/usr/sbin/sendmail -bd $SENDMAIL_OPTS $SENDMAIL_OPTARG (code=exited, statu    s=0/SUCCESS)
  ExecStartPre=/etc/mail/make aliases (code=exited, status=0/SUCCESS)
  ExecStartPre=/etc/mail/make (code=exited, status=0/SUCCESS)
 Main PID: 47008 (sendmail)
   CGroup: /system.slice/sendmail.service
           └─47008 /usr/sbin/sendmail -bd -q1h

systemd[1]: Starting Sendmail Mail Transport Agent...
sendmail[47008]: starting daemon (8.14.7): SMTP+queuei...00
systemd[1]: PID file /run/sendmail.pid not readable (y...t.
sendmail[47008]: NOQUEUE: SYSERR(root): opendaemonsock...se
sendmail[47008]: daemon MTA: problem creating SMTP socket
systemd[1]: Started Sendmail Mail Transport Agent.
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