Outlook 365 Server Reverse DNS Misconfigured: Microsoft please fix!

Running a mail-tester.com check on outgoing emails from my Outlook 365 account I get the following error:

Reverse DNS lookup or reverse DNS resolution (rDNS) is the determination of a domain name that is associated with a given IP address.
Some companies such as AOL will reject any message sent from a server without rDNS, so you must ensure that you have one.
You cannot associate more than one domain name with a single IP address.

Your IP address 40.107.10.132 is associated with the domain mail-eopbgr100132.outbound.protection.outlook.com.
Nevertheless your message appears to be sent from GBR01-LO2-obe.outbound.protection.outlook.com.

You may want to change your pointer (PTR type) DNS record and the host name of your server to the same value.

Here are the tested values for this check:
  • IP: 40.107.10.132
  • HELO: GBR01-LO2-obe.outbound.protection.outlook.com
  • rDNS: mail-eopbgr100132.outbound.protection.outlook.com

It's clear that this is not something that I can change myself. It's a bug that outlook has caused itself. Please fix asap, this is not acceptable for a supposedly reputable mail server as Outlook.

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Answer
Answer
Reply In reply to deleted message

Hi Cornelius Roemer,

Welcome to the community. For the phone support reply in your thread, please don't believe any information they provided. They're spamer and fake numbers, we have removed this abuse.

Regarding your situation, I want to tell you that setting up a PTR record is not supported by Office 365. Thus, it's not a bug and the truth is that your recipient domain has rejected your message. Office 365 is a shared environment that provides email service and the IPs are variable rather than fixed when sending emails via Office 365 SMTP server, it will return errors when the recipient email sever is using reverse DNS check.

More details, please see this article: Recipient rejects mail from Exchange Online or Exchange Online Protection, and you receive a "host name does not match the IP address" error

Best,

Shawn

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Last updated May 6, 2021 Views 2,394 Applies to: