Microsoft spent much of the past week rejecting legitimate emails sent to Outlook.com, Live, and Hotmail accounts due to what appears to be overly aggressive IP reputation filtering or faulty blocklist rules. According to The Register, many senders received 550 errors claiming their networks were blocked, preventing delivery of invoices, notifications, and authentication emails. From the report: A block list is a good thing. It helps stem the flow of spam from networks or addresses associated with junk email. However, the confusing thing for our reader is that his company was not on Microsoft's naughty step for email. 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)," our reader added, "which is intended to inform us when people are reporting spam sent from our IPs - except, we never get any reports." The problem worsened in February. On Microsoft's support forums, users began to complain about similar issues as the IP net presumably widened. One wrote: "We are currently experiencing a critical and recurring email delivery issue affecting recipients at outlook.com, live.com, hotmail.com, and msn.com," and provided a copy of an error that suggested the mail server has been "temporarily rate limited due to IP reputation." The user drily noted, "Although the error indicates rate limiting, in practice no emails are being delivered." A large number of users, ranging from the administrator of a server sending automated notifications on behalf of Estonian Public Libraries to an email provider for healthcare professionals, chimed in to confirm they too were having delivery problems and Microsoft support was not helpful. [...] Unsurprisingly, our reader spoke on condition of anonymity - nobody wants to be the ISP that has to say, "Yeah, we can deliver your email anywhere but Outlook.com" to customers. We asked Microsoft to comment, but other than acknowledging our questions, the company did not respond further.Read more of this story at Slashdot.