Emails to Outlook.com and Hotmail addresses have been failing to arrive in some cases since November 5, 2026. Windows Latest describes the case in a post from November 8 and was able to reproduce the rejection itself on the same day. t3n picked up the problem on November 9.
Instead of delivery, senders receive an error message from the mail server, such as „550 5.7.1 Message rejected: Message lacks SPF/DKIM/DMARC Auth Records“ or the code 550 5.7.23. The recipients learn nothing about the rejection.
Which emails are affected by the rejection?
Only a small share of emails is affected. Windows Latest cites senders with valid SPF, DKIM and DMARC records that were rejected anyway. Sending again sometimes got through. Senders using Zoho were also affected.
Microsoft has not confirmed a cause. Windows Latest found no indication of a deliberate change and names no confirmed solution.
What does Microsoft require of senders?
Since April 2025, Outlook.com, Hotmail and Live have had fixed rules for domains that send more than 5,000 emails per day. Such domains must pass SPF and DKIM checks and have a DMARC record with at least p=none. Microsoft announced that it would move non-compliant emails to the junk folder starting May 5, 2025, and later reject them with the code „550 5.7.515 Access denied“. A recipient's safe senders list changes nothing about this.
What Outlook.com requires of senders
Microsoft's rules for domains with more than 5,000 emails a day, announced for May 5, 2025
- SPF record lists all servers that send for your domain
- DKIM signature for your sender domain is active
- DMARC record is present, at least with p=none
- SPF or DKIM aligns with the domain of the sender address
- The recipient's safe senders list does not help
Microsoft has not confirmed whether the current case is related to this
Sources: Microsoft Tech Community, Windows Latest
The SPF record specifies which servers may send for your domain, including the service for your newsletter. DKIM signs every outgoing email. The DMARC record determines what happens to emails that fail both; with p=none, it only observes.
Whether the current case is related to the rule is unclear. The error message does mention SPF, DKIM and DMARC, but senders with correct records were also rejected. With normal email traffic, most self-employed people stay well below 5,000 emails a day; sending a newsletter, however, can reach that mark.
What this means for you
It is best to check the three records of your sender domain with an external testing tool before a customer asks. If the DMARC record is missing, create it with p=none: Windows Latest cites a Reddit user whose rejections disappeared after exactly this record.
If you send invoices or newsletters through an external service, the DNS records of your own domain must match that service. Microsoft explicitly makes this requirement of sending service providers.
If a customer with an Outlook or Hotmail address is waiting for a reply that never arrived, write to them through another channel and send the email again after a few minutes. Keep the complete error message: with it, your email provider or the Outlook.com support for senders can examine the case.
Windows Latest published the case on November 8, 2026.
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