"At the back end of January we noticed a sudden spike in customers static IPs being rejected by only Microsoft Outlook free / personal accounts. The message returned was a 550, telling customers to contact their Internet Service Provider (ISP) since part of their network is on our block list."
"A look at Microsoft's Smart Network Data Service (SNDS) showed no issues with the IP. We're also a member of their JMRP (Junk Mail Reporting Program), which is intended to inform us when people are reporting spam sent from our IPs - except, we never get any reports."
"We are currently experiencing a critical and recurring email delivery issue affecting recipients at outlook.com, live.com, hotmail.com, and msn.com. Although the error indicates rate limiting, in practice no emails are being delivered."
Microsoft experienced a significant email delivery problem affecting Outlook, Live, Hotmail, and MSN accounts when legitimate senders' IP addresses were incorrectly blocked or rate-limited. The issue began in late January with certain static IPs being rejected with 550 error messages, claiming the addresses were on Microsoft's block list. However, affected senders found no corresponding issues in Microsoft's Smart Network Data Service or spam reports through their Junk Mail Reporting Program. The problem escalated in February as more users reported critical delivery failures. Despite error messages indicating temporary rate limiting, no emails were actually being delivered. The situation affected diverse organizations including server administrators, email providers for healthcare professionals, and public library notification systems.
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