Have you ever wondered what happens when you send an email? Those messages travel through a complex system that routes them to the correct destination. Part of that system is DNS (or the Domain Name System). One of the functions of DNS is to keep track of email servers, and one way it does this is by using PTR records.
What Is a PTR Record?
A PTR record, or pointer record, is a type of DNS record that points to the hostname of an email server. An email server sends outbound message queries DNS for the associated PTR record to determine where to send the message. The recipient’s mail server checks the sending server’s PTR record to validate that the email address is not being used for a spam attack. If it finds what it believes to be a bogus PTR record, then that email is flagged as spam and may end up in your junk folder or never reach its destination at all. The domain name provider will take care of the reverse DNS PTR record for you.
How Can DNS PTR Records Help You?
If you are running your own email server, having a PTR record is essential. If you don’t have one, you run the risk of having legitimate emails marked as spam or even blocked completely. For example, let’s say that your company sends outbound mass mailings to clients using Exchange Server 2010. This may be marketing information, a new product release, or even an invitation to a company event. Without a PTR record, the receiving mail server might think that your email address is being spoofed and block it.
If you use a third-party email provider such as Gmail or Hotmail, you don’t need to worry about setting up a DNS PTR record. Technical support staff at the email provider will do that for you. They take care of this for you and have probably already set one up. It’s always a good idea to check with your web hosting provider before sending out any mass mailings just to make sure that they don’t have any special requirements or policies in place that might affect what you are doing.
Uses of a PTR Record
There are several other uses for PTR records and verifying email addresses. You can use them to:
Troubleshoot Mail Delivery Problems
When a receiving mail server rejects an email, the message is sent back to the sender. However, if that happens with your mass send emails and you have thousands of customers on your mailing list, then it could easily clog up your inbox for days. That’s where DNS PTR records come in handy.
Verify the Ownership of IP Addresses
You can also use PTR records to verify that an IP address belongs to a specific organization or company. For example, let’s say you are managing a large website that houses many smaller sites in subfolders. If those websites experience downtime and you receive complaints from your users, then checking the PTR record of an IP address can help you determine which site is having problems.
Check for Open Relays or Proxy Servers
If mail servers do not have an associated PTR record, it is probably an open relay or proxy server. Open relays are servers that allow anyone to send messages through them without any authentication required. It creates a huge security risk and makes those prime servers target spammers and hackers alike.
Detect Spam Traps
If you are sending out mass mailings to potential customers, then it is imperative that they are permitted to receive them. Otherwise, your messages will be seen as spam and may even get your IP address blocked by the recipient’s ISP. Unfortunately, many people do not pay attention when signing up for a service or filling out an online form and end up giving companies their email addresses without realizing what they have done. Spam traps work by identifying these so-called “human errors” to help keep the Internet free from junk mailers and other unsolicited content.
Aid in Email Authentication Schemes
Sender Policy Framework (SPF) and DomainKeys Identified Mail (DKIM) are two popular email authentication schemes that companies can use to confirm the identity of senders and prevent spoofing by unauthorized users. If you have a PTR record associated with your mail server’s IP address, then it will make these processes much easier because they rely heavily on reverse DNS lookups to validate messages before they are delivered.
Help With Reverse DNS Lookups
One of the main functions of a PTR record is to provide information about the hostname that is associated with an IP address. This makes reverse lookup possible, which can be used for a variety of purposes, such as troubleshooting mail delivery problems, verifying ownership of IP addresses, and detecting spam traps.
How To Set Up a PTR Record
Now that you know all about DNS PTR records and what they can be used for, it’s time to learn how to set one up. The process is actually quite simple, but there are a few things you need to take into account before getting started.
- Find out the reverse DNS name for your IP address: This can be done easily using a reverse DNS lookup tool such as the one provided by Google. Just enter the IP address and hit reverse lookup. If you are using a shared host account or VPS, then you will need to ask your hosting provider for the reverse DNS name of your server’s IP address. Domain registrars usually offer reverse DNS management tools in their control panels as well, so check with them first if they have any available options.
- Configure your domain’s reverse DNS: Now that you know the reverse DNS name for your IP address, you need to configure it on your domains. It is usually a very simple process requiring entering the correct information into a text field. However, not all domain name registrars offer this service, so be sure to check before signing up. Top level domains, for example, “.com”, offer reverse DNS services at an additional cost.
- Create a PTR record: Once you have the reverse DNS name or domain names and your domain’s registrar has been updated, you can create a PTR record. This is usually done through the same interface where you manage other DNS records for your arpa top level domain. Just enter in the reverse DNS name and select the correct TTL value. IP address reverse lookup is the process of having a query DNS record that maps an IP address back to a hostname. PTR1 records (pointer records) are used to perform this lookup.
- Testing PTR Records: Once you are done creating your new PTR1 record, it will take some time for it to propagate throughout the Internet. You can use a tool such as Mxtoolbox to test whether or not it is working correctly. Just enter in the IP address and hit “lookup.” If everything is set up correctly, you should see the hostname associated with that IP address in the results. Host that PTR1 points to reverse DNS name PTR record.
Final Words
PTR records are an important part of reverse DNS lookup, which in turn can be used for a variety of purposes, such as troubleshooting mail delivery problems and detecting spam traps. They also play an integral role in email authentication schemes like SPF and DKIM.
Setting up reverse DNS records is usually very simple but does require some knowledge about how reverse DNS works before getting started.
