How do specify the PTR for the email to work correctly?

When you receive an error in the mail server log associated with PTR records, for example:

Action: failed
Final-Recipient: rfc822;*@gmail.com
Status: 5.0.0
Remote-MTA: dns; gmail-smtp-in.l.google.com
Diagnostic-Code: smtp; 550-5.7.25 [*] The IP address sending this message does not have a
550-5.7.25 PTR record setup, or the corresponding forward DNS entry does not
550-5.7.25 point to the sending IP. As a policy, Gmail does not accept messages
550-5.7.25 from IPs with missing PTR records. For more information, go to
550 5.7.25 https://support.google.com/mail/answer/81126#ip-practices i4-20020a05600c354400b0040e968c2d11si6832247wmq.130 - gsmtp

You need to pay attention to the error description and the link that the mail server that rejected your email offers to read. Usually, the letter contains comprehensive information about the reasons for the cancellation of the delivery of the letter and options for solving this difficulty.

In case of such an error, you need to make sure that the server settings contain the correct PTR record, which indicates its IP address and corresponds to the HELO response of your server. You can specify the PTR by following [this instruction].

You can check the server's HELO by using the telnet command, adding your server's IP address and port 25, for example:

telnet 1.1.1.1 25

The command will return a response in the format:

220 test.chost.com.ua ESMTP Exim 4.94 Wed, 24 Jan 2024 10:58:05 +0200

where test-chost.com.ua is the PTR that you need to set in the server settings. Please note that 1.1.1.1 and test.chost.com.ua are just examples, you need to substitute your own data.