How to Fix The 554 Invalid PTR Resource Record Error?

How to Fix The 554 Invalid PTR Resource Record Error?

How to Fix The 554 Invalid PTR Resource Record Error?

Working with emails can be challenging at times. 554 Errors are common and hard to deal with. If you’re getting the 554 Invalid PTR Resource Record Error, then you’re not alone. Many server administrators receive this even after making necessary changes to their IP address and DNS records. But this error has to do with Reverse DNS, which is also known as PTR. In this article, we’ll explain how to work around this error to get your email services back on track.

What is PTR Record?

A PTR Record is the direct opposite of DNS or Domain Name Server. PTR stands for Pointer Record and is an integral part of email server systems. In case of DNS, domains are pointed to their respective IP addresses. But in case of PTR, reverse is true, i.e. IP addresses are associated with their respective domains. These records are used to check if the server is associated with the IP address which initiated the connection. This is an important security protocol both intermediate mail servers and dedicated mail servers follow.

When a mail is send from the sender, it goes through his/her MX, then the recipient’s MX, before finally getting delivered to recipient. If at any of the levels, there’s an error with the PTR, then you’ll get the 554 Invalid PTR Record Error with messages like:

Code: (hostname) ESMTP Service not available
554-No SMTP service
554 invalid DNS PTR resource record, IP=303.0.123.1
Service not available 554-No SMTP service 554-Bad DNS PTR resource record.

What causes the PTR error and how to fix them?

The error occurs primarily when:

The sender has migrated to a new Datacenter and RDNS hasn’t been configured yet.

The server sending the emails has a new IP, but with no PTR records.

There’s a network delay which in turn causes DNS lookup error

In each of the above scenarios, the common causes of this error are:
  • Missing PTR Record
The servers were not able to verify the PTR records because there were none in the first place. It’s common for web hosts to not set PTR records for the assigned IP after server migration. With the PTR missing, mail servers treat your IP as spam and hence block the transmission. To fix this problem, you simply have to add a PTR record.

But just to make sure, let’s check if the PTR record exists or not. For that use the following code:

dig -x
This will reveal the RDNS entries. If there’s none, you need to get the correct PTR records for your IP address. Your mail server provider will get you the records. If an external DNS server is employed, then also you’d have to add in the PTR records.
  • Invalid PTR Records
If the above code confirms that there is PTR record in place for your IP address and you’re not able to send emails, then chances are the PTR is invalid.

A common trend we’ve seen with most host providers is they assign a generic PTR for every IP address which is like: “xxx-xxx-xxx-xxx-host.provider.tld”

But when it gets generic for every IP address, then other mail servers treat this as spam since it gets into thinking that this is a dynamic IP address.

To solve this problem, you have to change the PTR from a generic to an FQDN (Fully Qualified Domain Name). An example of this is

If it’s a Virtual Private Server hosting multiple domains on the same IP address, you can select the unique hostname of the server and use it as PTR record.

If problem persists, we recommend you to get in touch with your mail host provider for assistance.
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