Users fume at Outlook.com email 'carnage'

Email flow slowed or stopped by mysterious forces at Microsoft

Updated Microsoft spent last week rejecting emails to Outlook recipients after what appears to be either a fault or overzealous blocking rules.

The problem affects certain IP addresses, whose emails are rejected due to falling foul of reputation rules or appearing on a block list.

A Register reader told us, "At the back end of January we noticed a sudden spike in customers static IP's 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 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 glance 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 went on, "which is intended to inform us when people are reporting spam sent from our IP's - 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 that 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 that they, too, were having delivery problems and that Microsoft support was not helpful.

Our reader told us, "We've seen customers struggling to send invoices, order delivery notifications, authentication codes - all sorts, which have been perfectly acceptable to Microsoft / Outlook for many years - now rejected, or blocked.

"Customers rarely read, or understand DSN's - they jump to blaming the ISP or sender, and then head off to find someone else."

Unsurprisingly, our reader spoke on condition of anonymity. After all, 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 if it had any comment to make, but other than acknowledging our questions, the company did not respond.

Blocking email from spammers is a good thing, and anything that reduces the amount of junk that clutters up inboxes is to be applauded. However, when there is an error, customers need a rapid and transparent process for resolution. Every failed delivery of an invoice or receipt due to overzealous or misapplied rules can chip away at a business's reputation, through no fault of the owner. ®

Updated at 13.33 UTC on March 6, 2025, to add:

Microsoft has finally responded, days after this article was published. A spokesperson told The Register:

"We are working to address a temporary rate‑limit issue that may be causing some messages to be incorrectly throttled when sent from a specific IP address. Customers who continue to experience issues sending emails should contact our Support team or raise a ticket in their Admin portal to apply the appropriate mitigation."