Someone at Microsoft should come up with an explanation for a messed-up DNS record that caused emails sent from Microsoft Outlook Hotmail accounts to be dropped and end up in spam folders since Thursday.
Late Thursday afternoon, Hotmail users began reporting that some emails were being returned with Sender Policy Framework (SPF) errors, so recipients' email services could not "verify that the message came from a trusted location."
SPF, for those who don't know, is an outgoing email authentication method that helps prevent email spoofing, impersonation, and phishing. If, for example, a service like Hotmail removes one of the subdomains from DNS TXT that has SPF, then the recipient's services will consider emails coming from that subdomain to be spam.
Reddit users posting to the Sysadmin subreddit verified the SPF problems with Hotmail. A user uploaded Hotmail's SPF file and found that Redmond had made two changes: it removed spf.protection.outlook.com and changed the SPF failure condition from soft to hard. This meant that any suspicious messages from Hotmail would have to be rejected rather than simply sent as spam.
Microsoft support forum advisors confirmed that the issue is known. According to Microsoft: "Some users may receive non-delivery reports when trying to send email from hotmail.com."
"We've found that additional entries are affected and are implementing further changes to resolve the issue," Microsoft says. Shortly after Microsoft Reported that the changes are complete and the problem is fixed.