Fix The 554 Invalid PTR Resource Record Error
554-554-bad dns ptr resource record - (hostname) ESMTP Service not available
554-No SMTP service - 554 invalid DNS PTR resource record



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 recipients MX, before finally getting delivered to recipient. If at any of the levels, theres an error with the PTR, then youll get the 554 Invalid PTR Record Error with messages like:

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

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 a normal mail delivery, mail goes from the sender, to the sending MX, and to the recipients MX, and finally to the recipient. 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 senders authenticity, it rejects such emails and users see the bounce message as below. 554-No SMTP
service 554 invalid DNS PTR resource record

ts obvious that you have a doubt, whats 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 senders PTR record, and either it cant find the hostname of the IP address,
or the hostname it found doesnt resolve to the same IP.

-------------------------------------
:
-------------------------------------

The sender has migrated to a new Datacenter and RDNS hasnt been configured yet.
The server sending the emails has a new IP, but with no PTR records.

The servers were not able to verify the PTR records because there were none in the first place. Its 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.
A common trend weve 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.
, 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.

-------------------------------------
:

-------------------------------------

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 abc.yourservername.com.

If its 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.

Conclusion

In short, 554 invalid DNS PTR resource record ocurs due to missing or invalid PTR records. In both cases,
users cant do much other than contact web hosts or ISPs.



ptr terminal

11.22.33.44


:
dig PTR 44.33.22.11.in-addr.arpa

--------------------------------------------------------
ptr CMD

:
nslookup 11.22.33.44


--------------------------------------------------------
DNS

http://leafdns.com

:
https://hoststud.com/resources/how-t...ord-error.670/
https://bobcares.com/blog/554-invali...source-record/
https://www.godaddy.com/help/what-is-reverse-dns-2585
https://community.spiceworks.com/top...ecific-address
https://docs.cpanel.net/knowledge-ba...ng-ip-address/
https://support.cpanel.net/hc/en-us/...tom-mail-HELOs