Aug 20 2023

Microsoft DNS boo-boo breaks Hotmail for users around the globe

Category: DNS Attacks,Information Securitydisc7 @ 11:05 pm

Someone at Microsoft has some explaining to do after a messed up DNS record caused emails sent from Hotmail accounts using Microsoft’s Outlook service to be rejected and directed to spam folders starting on Thursday.

Late on Thursday evening, Hotmail users began reporting that some emails were being returned with errors related to Sender Policy Framework (SPF), and thus recipient email services were unable “to confirm that [a] message came from a trusted location.” 

SPF, for those unfamiliar with it, is a method of outbound email authentication that helps avoid email spoofing, impersonation and phishing. If, for example, a service like Hotmail were to have one of its subdomains removed from the DNS TXT record that stores its SPF list, then recipient services may assume it’s junk. 

And that appears to be just what happened. 

Reddit users posting to the Sysadmin subreddit verified they were experiencing SPF issues with Hotmail. One user pulled up Hotmail’s SPF record and found that Redmond had made two changes: removing from the record, and changing the SPF failure condition from soft to hard. That meant any suspicious messages from Hotmail should be rejected rather than just sent to spam. 

Microsoft support forum advisors confirmed that the issue was known, which was further confirmed by a look at the Office service status page. Per Microsoft: “Some users may receive non-delivery reports when attempting to send emails from” 

At time of writing, the status page indicated that “a recent change to email authentication” was the potential root cause of the outage. Microsoft said it made a configuration change to remediate impact, but shortly after said the problem may have been worse than it appeared at first glance. 

“We’ve identified that additional configuration entries are impacted, and we’re implementing further configuration changes to resolve the issue,” Microsoft said. Not long after that was posted, Microsoft indicated configuration changes were complete and the problem was fixed. 

Microsoft didn’t respond to our questions about the incident, only saying the issue had been resolved.

Tags: Microsoft DNS