We're seeing this as well. Here are some details/lookups on a sample Office 365 ip: https://www.misk.com/tools/#dns/40.107.66.111
Reverse dns is fine, forward lookup fails intermittently due to a nameserver referral loop: https://www.misk.com/tools/#dns/mail-eopbgr660111.outbound.protection.outlook.com https://www.misk.com/tools/#dns/mail-eopbgr660111.outbound.protection.outlook....@ns1-gtm.glbdns.o365filtering.com https://www.misk.com/tools/#dns/mail-eopbgr660111.outbound.protection.outlook....@ns2-gtm.glbdns.o365filtering.com Keep hitting refresh and you'll see the issue. Eventually, their auth servers return an ip. Looks like one or more (but not all) of the auth dns servers in their dns farm is misconfigured, which is why it is intermittent. You can also run dig multiple times from your local machine and you can see it there as well: dig mail-eopbgr660111.outbound.protection.outlook.com @ns1-gtm.glbdns.o365filtering.com dig mail-eopbgr660111.outbound.protection.outlook.com @ns2-gtm.glbdns.o365filtering.com If anyone has a contact there on the right team, please forward. Thanks, Nitin Agarwal nagar...@misk.com https://www.misk.com/ https://www.misk.com/tools/ -----Original Message----- From: mailop <mailop-boun...@mailop.org> On Behalf Of Neil Youngman via mailop Sent: Monday, August 23, 2021 9:16 AM To: mailop@mailop.org Subject: [mailop] Microsoft RDNS issues Is anybody else seeing issues with some Microsoft RDNS failing intermittently. I'm seeing RDNS failures in our Exim logs, but when I check the IPs from the command line, there are no obvious issues and it isn't affecting all our traffic from Microsoft. It seems t have started a little before midnight on Friday. I'm not seeing anything similar with mail from Google or Messagelabs, which is why I think it's somewhere external to us. Neil Youngman Neil Youngman Developer [Logo]<https://www.wirefast.com/> T: +44 (0)20 7092 8460 E: neil.young...@wirefast.com W: www.wirefast.com<http://www.wirefast.com> Wirefast Limited | 19 Bedford Row, London | WC1R 4EB. ________________________________ Wirefast provides secure corporate messaging services. See our messaging solutions at https://www.wirefast.com/ Please consider the environment. Does this email or attachment need to be printed? This message contains confidential information and is intended only for the individual named. If you are not the named addressee you should not disseminate, distribute or copy this email. Please notify the sender immediately by email if you have received this email by mistake and delete this email from your system. Any views or opinions are solely those of the author and do not necessarily represent those of Wirefast Limited Email transmission cannot be guaranteed to be secure or error-free as information could be intercepted, corrupted, lost, destroyed, arrive late or incomplete, or contain viruses. The sender therefore does not accept liability for any errors or omissions in the contents of this message which arise as a result of email transmission. Wirefast Limited is registered in England & Wales Company number: 03865860 Registered Office: 7/10 Chandos Street, Cavendish Square, London, W1G 9DQ Wirefast definitions of classification can be found here: https://www.wirefast.com/classifications/<https://www.wirefast.com/classifications> _______________________________________________ mailop mailing list mailop@mailop.org https://list.mailop.org/listinfo/mailop _______________________________________________ mailop mailing list mailop@mailop.org https://list.mailop.org/listinfo/mailop
