Email errors are quite irritating, especially if they are abstruse like this “554 invalid DNS PTR resource record“.

Here, the error message shows that the recipient rejects the email because of the invalid PTR record.

But, what’s this PTR record? Do I have to set it from my end?

Don’t worry, at Bobcares, we help website owners resolve such email errors as part of our Outsourced Technical Support services for web hosts.

Today, we’ll discuss the top 2 reasons for this error and the steps to resolve this issue.

“554 invalid DNS PTR resource record”- What this means?

In a normal mail delivery, mail goes from the sender, to the sending MX, and to the recipient’s MX, and finally to the recipient.

How email works?

But, sometimes not all emails reach the destination server. The recipient server performs a series of checks such as PTR or reverse DNS checks, SPF checks, etc. to prevent fraud emails.

If the recipient server has doubt in the sender’s authenticity, it rejects such emails and users see the bounce message as below.

554-No SMTP service 554 invalid DNS PTR resource record

It’s obvious that you have a doubt, what’s this PTR record in the message?

Well, PTR records aka Revers DNS map IP address to domain name and helps to validate a user.

That is, if a server “xyz.servername.com” points to IP address “195.xxx.12x.10x“, the PTR record of the IP should be “xyz.servername.com“.

So, here the recipient server checks the sender’s PTR record, and either it can’t find the hostname of the IP address, or the hostname it found doesn’t resolve to the same IP.

“554 invalid DNS PTR resource record” – Causes and Fixes

Based on our experience managing servers, this error occurs mainly in the following cases.

• The sending server has recently migrated to a new Datacenter that doesn’t have RDNS set.
• The sending server has assigned a new set of IPs with no PTR records.
• Network delay or DNS lookup errors.

Now, let’s see the common causes of this error and how our Dedicated Support Engineers fix it.

1) Missing PTR record

Most of the times, web hosts fail to set PTR records for IPs after server migration, new IP assignment, etc.

But, most major email providers like Hotmail, use this as an important indicator of the source of spam.

So, if PTR entry is missing, mail servers deny transport considering this as a major signal of spam.

Solution

Firstly, our Hosting Engineers verify that a PTR record exists for the IP address using the below command.

dig -x 195.xxx.12x.10x

If we find missing RDNS entries for the IP address, we’ll add the correct PTR record for the IP address.

Alternatively, when an external DNS server is used, we update the customer to contact their ISP to add appropriate PTR records.

At Bobcares, we always configure critical mail records such as PTR, SPF, DKIM, etc. to ensure that mail delivery errors are avoided.

[Problems setting up PTR records for your domain? Our Support Experts can help you here.]

2) Invalid PTR record

Similarly, another common trend is that web hosts set generic PTR records for IPs like “xxx-xxx-xxx-xxx-static.provider.tld“.

But, these generic rDNS records get rejected at various email service providers.

Because, the remote mail server thinks that this is a dynamic IP address, due to the format of the PTR record with the encoded IP, and hence rejects the connection.

Solution

In this case, our Support Engineers first verify that the PTR record set for the domain is a generic one using the dig command.

If it’s generic, we change that PTR record to an independent and fully qualified domain name(FQDN) of the host.

For example, xyz.servername.com.

Likewise, in VPS servers, if multiple domains are hosted on the same IP address, we pick the hostname of the server and use that as the PTR record.

And, all other domains act as aliases of this original domain.

[And, you need help to fix this error? Our Hosting Experts can fix this for you.]

Conclusion

In short, “554 invalid DNS PTR resource record” ocurs due to missing or invalid PTR records. In both cases, users can’t do much other than contact web hosts or ISPs. Today, we’ve discussed the top 2 reasons for this error and how our Dedicated Support Engineers fix it.