Why did Microsoft 365 block Google’s and LinkedIn’s domain? What is MO255463?
“Your most unhappy customers are your greatest source of learning.” – Bill Gates
Microsoft issued an advisory (MO255463) notifying its users and admins that a Microsoft 365 bug has resulted in a massive flow of legitimate emails sent from multiple domains (including Google and LinkedIn) getting tagged as malicious and quarantined.
We’re investigating an issue with email flow, links within email messages and the Microsoft Defender portal. We’ve identified the cause and performed actions to mitigate impact for new emails…. continued….
— Microsoft 365 Status (@MSFT365Status) May 10, 2021
Impact Of The Microsoft 365 Bug
- inability to send/receive email from various domains (incl. Google & LinkedIn)
- quarantining legitimate emails
- inability to access links within emails as they’ve been flagged as ‘high risk’
- users potentially getting blocked for sending emails if messages are incorrectly classified as spam or phishing
According to Microsoft, this whole unfortunate fiasco has been associated with –
- an increase in the number of URL-related alerts for non-malicious URLs
- an increase in the number of Zapped Phish AIR investigations in Microsoft Defender
- legitimate emails being marked as malicious in Threat Explorer
- delays in getting the latest email information in Threat Explorer
This year definitely didn’t get off to a good start for Microsoft. First, it was the Microsoft Exchange hack dubbed “The Greatest Email Heist” back in March. Then the FBI got involved with a court-authorised fix for the hack. Not to mention Egress’ research stating that 85% of organisations using Microsoft 365 have had an email breach in the last 12 months.
Microsoft reported all issues – including the current one – have been fixed, but… how long until another hack or “issue” comes along threatening the email data security of millions of organisations and individual users?
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