PTR Record Overview

Reverse resolution means to obtain a domain name based on an IP address. This is typically used to affirm the credibility of email servers.

After a recipient server receives an email, it checks whether the IP address and domain name of the sender server are trustworthy and determines whether the email is spam. If the recipient server fails to obtain the domain name mapped to the sender's IP address, it concludes that the email is sent by a malicious host and rejects it. Therefore, it is necessary to map IP addresses of your email servers to domain names by adding PTR records.

**Table 1** PTR record description
Operation	Scenario	Constraints
Creating a PTR Record	Create PTR records for cloud resources such as ECS.	PTR records are project-level resources. When you create a PTR record, you need to select a region and project. You can add up to 50 PTR records in your account.
Managing PTR Records	Modify, delete, batch delete, or query PTR records.	After a PTR record is created, the EIP cannot be changed. After you delete a PTR record, the domain name mapped to the EIP will change to the default domain name.