Updated 4/29/25 to accommodate Microsoft’s new changes
We knew it was coming eventually.
Valimail previously reported that Microsoft indicated that updated sender requirements were likely to be announced at some point in the future, and that time is now.
Microsoft announced it will join Google and Yahoo in updating their email sender requirements. This will raise the bar to help better protect email inboxes by making email authentication a prerequisite for successful email delivery to Microsoft inboxes.
However, there’s one key difference. Starting May 5, 2025, Microsoft announced that it will actively begin rejecting mail that doesn’t meet its published requirements for bulk senders.
This is a hard deadline, unlike the slower rollouts and warning-phase approaches we’ve seen in the past. And for many senders, it’s a wake-up call to prioritize these requirements.
“Outlook has always prioritized user safety and reliability; we’re proud to further invest in this solution that will keep our customers safe and reinforce the best practices across the industry. We believe that by raising the bar for large senders, we can inspire lasting change that benefits everyone.”
– Microsoft’s announcement
Microsoft’s requirements are a clear market signal
This is the most visible and significant enforcement action yet, and it will cause real pain for non-compliant senders. That’s the point, and the signal the market needs to take authentication seriously and complete the journey.
Google and Yahoo laid the foundation, but Microsoft has taken it another step further by making the consequences clear and unavoidable.
As Microsoft joins the growing number of global mailbox providers requiring strong authentication to protect global email – safeguarding consumers and companies from spam, phishing, and abuse – Valimail takes pride in being a standard bearer of this message for the past decade.
We’ve watched this landscape evolve from when we stood alone championing the need for authentication to be accessible for senders of all sizes to seeing authentication become the law of the land.
Today, email authentication is a requirement for anyone sending email messages at scale, with the three largest mailbox providers (Google, Yahoo, and Microsoft) now agreeing that it should be required across the board for all. Microsoft’s new requirements mirror similar sender mandates previously put forth by Google and Yahoo. Now, more than ever, email authentication (and DMARC) is required for successful email senders.
While the focus today is on consumer inboxes, Microsoft said it would eventually extend to enterprise as well.
“Microsoft’s commitment to sender requirements – matching what Google and Yahoo have already established – demonstrates that strong authentication isn’t just a best practice anymore, it’s the new law of the land. This has tremendous impact for senders of all sizes, from their security practitioners to marketers and everyone in between. When you authenticate your mail, you get the deliverability you deserve. Without authentication, you get rejected.”
– Seth Blank, CTO of Valimail
What are Microsoft’s new requirements?
Anyone sending more than 5,000 email messages per day to these top consumer mailbox providers – Google’s Gmail, Yahoo Mail, and/or Microsoft’s Outlook.com (covering the domains live.com, hotmail.com, and outlook.com) will need to comply with these sending requirements.
- Authenticate all emails using both:
- SPF (Sender Policy Framework)
- DKIM (DomainKeys Identified Mail)
- Publish a DMARC record with a policy of p=none or stronger
- Ensure alignment between DMARC and either SPF or DKIM (Microsoft recommends both be aligned)
- Use valid From and/or Reply-To addresses that can receive replies
- Include a functional unsubscribe link in messages where appropriate
- Maintain transparent mailing practices, including:
- Avoid deceptive headers or practices
- Send only to users who have consented
- Employ proper list hygiene
- Handle bounces effectively
Senders must comply with these requirements by May 5, 2025. Microsoft has clarified that mail sent that does not follow these guidelines will be rejected.
Email authentication (and DMARC) now required
All email messages must pass Sender Policy Framework (SPF) and DomainKeys Identified Mail (DKIM) email authentication checks. Microsoft (along with Yahoo and Google) utilize these checks to validate email message integrity and authenticity.
Additionally, sending domains must have a published DMARC policy, with a policy setting of p=none or better, and there must be proper alignment with either SPF or DKIM authentication settings (Microsoft’s guidelines recommend both be aligned whenever possible).
Senders who aren’t able to comply with these SPF, DKIM, and DMARC email authentication requirements will struggle to reach the inbox and are likely to see their email rejected in the near future.
Additional sender requirements
Microsoft additionally requires that the From and/or reply-to addresses be valid and that they must be able to receive replies. Messages must contain functional unsubscribe links as appropriate, making it easy for recipients to opt out of further email communications.
Transparent mailing practices are required. Avoid deception, ensure that you have consent, employ appropriate list hygiene best practices, and process bounces properly.
What happens if your email is not compliant
If your mail doesn’t comply with these email sender requirements, it will be rejected and not delivered to its intended address.
You’ll receive an error code from Microsoft, similar to this:
“550; 5.7.515 Access denied, sending domain [SenderDomain] does not meet the required authentication level.” Microsoft’s enforcement date is approaching, and the company has made it clear that it takes these guidelines seriously. There’s little time left to set up your domains to send successfully, but Valimail can help.
How Valimail can help you meet these requirements
The Microsoft changes are already in motion, and the deadline is fast approaching. If you wait, your consumer email won’t be delivered to Microsoft inboxes. If you act now, you can turn this moment into a strategic advantage.
As champions of DMARC and Microsoft’s go-to solution for DMARC and hosted SPF, Valimail is uniquely positioned to help senders navigate this new era of enforcement. It’s what we do best.
We’re the #1 market leader in DMARC, and we helped many customers meet the previous Google and Yahoo requirements.
“Valimail has a free monitoring tool so you don’t have to jump into the deep end right away. You can really identify if you have significant issues that need to be investigated further. The DMARC changes for Google and Yahoo set off this firestorm, and I am by no means a DMARC expert. Valimail graciously taught me the basics!”
– Damon P, G2 Review
We believe that visibility into your domain should always be free. With no trials, credit cards, or obligations, you can create your own Valimail Monitor account and enjoy these features:
- Instantly assess your compliance with Microsoft’s requirements
- Spot authentication gaps across SPF, DKIM, and DMARC
- Take the first critical step towards DMARC enforcement
