SMTP greeting contains the hostname only: lost connection while performing the HELO handshake

Symptoms

• Send from domain IP addresses and use domain names in SMTP greeting option is enabled in Tools & Settings > Mail Server Settings
• SMTP greeting contains the server hostname only
• The following record might be found in /var/log/maillog file:
  

  CONFIG_TEXT: postfix/smtp[30864]: 4F7921800D93: to=<john.doe@example.com>, relay=mail.example.com[203.0.113.2]:25, delay=306940, delays=306940/0.07/0.14/0, dsn=4.4.2, status=deferred (lost connection with mail.example.com[203.0.113.2] while performing the HELO handshake)

• Online tool mxtoolbox.com shows the following:
  

  CONFIG_TEXT: Reverse DNS does not match SMTP Banner

• There is no PTR record for domain:
  

  # dig PTR example.com
  ;; QUESTION SECTION:
  ;example.com. IN PTR
  ;; AUTHORITY SECTION:
  example.com. 7931 IN SOA ns02.hostname.com. hort\.hostname.com. 1511348154 10800 3600 604800 10800

Cause

PTR record is not configured for the domain.

Resolution

Contact ISP to setup a reverse (PTR) record that matches the hostname of mail server.

Additional information

What hostname should be specified in PTR record?

How to add PTR record to Cloud Server with installed Plesk?

SMTP Banner Check