Running a mail-tester.com check on outgoing emails from my Outlook 365 account I get the following error:
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 22.214.171.124 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: 126.96.36.199
- 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.