Overview

What is a PTR Record?

A PTR record provides the domain name associated with an IP address. It is the opposite of a regular DNS lookup. PTR records are used in many network applications. For example, email servers use reverse resolution to verify the sender's IP address to reduce spam and network fraud.

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. It is necessary to configure pointer records (PTR) to point the IP addresses of your email servers to domain names.

Reverse Resolution Process

In the following figure, an ECS serves as an email server, and a PTR record is configured to map the EIP of the ECS to the domain name configured for accessing the email server.

Figure 1 Reverse resolution
Click to enlarge

Figure 1 shows only the process for reverse resolution. Information about how an email server checks the credibility of the sender's IP address and whether the domain name is available on the Internet is not provided here.

If no PTR records are configured, the recipient server will treat emails from the email server as spam or malicious and discard them. Therefore, if you want to build an email server, it is necessary to add a PTR record to map the email server IP address to your domain name.

Related Operations

**Table 1** PTR record operations
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.