Starting May 5, 2025, Microsoft Outlook is imposing new authentication and email hygiene requirements for high-volume senders. If your domain sends more than 5,000 emails per day and your email infrastructure or email lists aren’t up to par, your campaigns could quietly disappear into the spam folder. Or worse: be blocked altogether.
While the headlines focus on SPF, DKIM, and DMARC, there is another part of this update that deserves attention: list hygiene.
What is changing?
According to Microsoft’s announcement , the new rules b2b email list apply to anyone who sends more than 5,000 messages per day to Outlook.com, Hotmail, and Live.com addresses. This is part of a broader industry shift to make email more secure, more transparent, and less susceptible to abuse.
high-volume senders must now:
Authenticate sending domains using SPF, DKIM, and DMARC .
Please use a functional and visible unsubscribe fax list link in every email.
Make sure your “From” and “Reply-To” addresses publish your content are valid and monitored.
Maintain clean, consent-based subscriber lists , with low bounce and complaint rates
Microsoft is clear: senders who don’t comply will not only suffer drops in engagement, but will see their emails diverted to spam or rejected.