Hotmail users worldwide have been experiencing email delivery problems after Microsoft misconfigured the domain’s DNS SPF record.

The email issues began late last night, with users and admins reporting on Reddit, Twitter, and Microsoft forums that their Hotmail emails were failing due to SPF validation errors.

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SPF is a security mechanism that helps to prevent email spoofing. It works by allowing email servers to verify that an email is actually coming from the sender it claims to be from. When Microsoft misconfigured the DNS SPF record, it caused email servers to reject Hotmail emails as spam.

Microsoft has acknowledged the issue and said that they are working to fix it. In the meantime, Hotmail users may experience delays in email delivery.