Recently, Microsoft changed mail flow rules related to Office 365 (O365) accounts that may have affected the May phishing test email deliverability. Microsoft instituted greylisting, also known as IP throttling. This has directly affected our partners’ and clients’ test results showing very low open rates.
For more information, see the link below. https://docs.microsoft.com/en-us/exchange/mail-flow-best-practices/non-delivery-reports-in-exchange-online/fix-error-code-451-4-7-500-699-asxxx-in-exchange-online
What You Need To Do:
In the Microsoft documentation linked above, Microsoft outlined the process of resolving the 451 error by adding a Connector to O365 accounts in order to ensure mail delivery from third-party senders.
How to setup a Microsoft Connector and Resolve 451 Error:
Please configure the Microsoft Connector to be prepared for June testing. If you would like to re-run your May test, please create a ticket at firstname.lastname@example.org or call Amanda Arias at (864) 727–0771
Stay aware, out there!
- The Hook Security Team