Unable to send mail messages from example.com to particular domain with the following error in
Dec 1 04:09:54 hostname postfix/smtp: 890201800C1C: to=<[email protected]_domain.com>, relay=mail.some_domain.com[203.0.113.100]:25, delay=244006, delays=244006/0.01/0.07/0, dsn=4.4.2, status=deferred (lost connection with mail.some_domain.com[203.0.113.100] while performing the HELO handshake)
Messages to other domains are delivered successfully.
Checking RDNS for mail server IP shows that several domains are associated with IP:
# dig +short mail.example.com
# dig +short -x 203.0.113.2 | wc -l
Server hostname resolves to the same IP:
# dig +short server_hostname
PTR record is added to DNS Template under Tools & Settings > DNS Template ;
Misconfiguration of Reverse DNS, so the sent message does not pass the validation procedure for incoming SMTP connections on the recipient side.
The best practice is when reverse DNS request returns the server’s hostname, which by default is the same as mail server hostname.
To configure PTR correctly follow the steps:
- Delete all PTR settings from DNS Template and apply the changes;
- Create a domain in Plesk with name “server_hostname”;
- Create PTR record for the domain under Domains > server_hostname > DNS settings, which points to 203.0.113.2.
- Check Send from the specified IP addresses (203.0.113.2) option under Tools & Settings > Mail Server Settings :