Microsoft Outlook’s New Requirements for High‐Volume Senders [2026 Update] — What You Need To Know

Following Google (Gmail) and Yahoo’s crackdown on bulk email senders in 2024, Microsoft Outlook is tightening the rules for high-volume senders from May 5, 2025. If you’re sending bulk messages (more than 5000 emails a day) to customers, clients, or subscribers through Outlook, ignoring these updates could land your messages straight in the junk folder or worse—get your domain throttled or blocked.

In this article, we will break down everything you need to know about Microsoft Outlook’s new requirements for high-volume email senders, why Microsoft made these changes, and what practical steps you can take to protect your sender reputation and maintain email deliverability.

Ready? Let’s get started!

NOTE: These requirements will only apply to Outlook, which includes Outlook.com, Hotmail.com, and Live.com.

What Are Microsoft Outlook’s New Sender Requirements?

On April 2, 2025, via a Microsoft community blog, they announced the enforcement of email authentication protocols for all senders who send large volumes of email (more than 5,000 emails a day) through Outlook.

This update is part of a broader effort to combat spam, phishing, and spoofing, which continue to be widespread problems.

If you’re sending over 5,000 emails per day, here’s what you now need to pass:

• SPF (Sender Policy Framework): Your DNS must list all legitimate IPs allowed to send mail on your domain’s behalf.
• DKIM (DomainKeys Identified Mail): To verify the integrity and authenticity of your email, you must have a DKIM record set up.
• DMARC (Domain-based Message Authentication, Reporting, and Conformance): Your domain needs a published DMARC record with at least a p=none policy, aligned with SPF or DKIM (preferably both).

NOTE: Enforcement begins May 5, 2025, and the first wave of non-compliant emails will be rerouted to recipients’ Junk folders. Later, Microsoft plans to outright reject these emails.

Let’s Understand Outlook’s New Sender Requirements in Detail 

SPF, DKIM, and DMARC are the industry-standard email authentication protocols that verify the integrity and authenticity of both the sender and the content of an email.

According to Google, after implementing email authentication requirements, 265 billion fewer unauthenticated messages were sent in 2024.

Microsoft is now holding senders accountable for securing their outbound emails. So, let’s understand these protocols in detail:

SPF (Sender Policy Framework)

SPF is your domain’s way of saying, “These are the IP addresses allowed to send email on behalf of me.” In other words, if an email sent from your domain is coming from an IP address listed in your DNS record. If the sending server is not listed in the SPF record, the message fails SPF checks.

To meet the SPF record requirement:

• You must publish an SPF record in your DNS settings.
• That record should clearly list all sending IPs and domains.
• Keep SPF under 10 DNS lookups to avoid automatic failures.

A valid SPF record looks something like this: v=spf1 include:_spf.google.com ~all

To learn more about SPF Records, check our detailed blog on What is an SPF Record? How Does It Work [Ultimate Guide] 

DKIM (DomainKeys Identified Mail)

DKIM attaches a cryptographic signature to each email, which the recipient’s server can verify using your domain’s public key published in DNS. It’s like sealing a letter in wax: if the seal is broken, something’s wrong.

For you to meet the DKIM requirements:

• Each outgoing message must include a valid DKIM signature.
• This signature proves the message hasn’t been tampered with in transit.
• Set up DKIM through your DNS with public/private key pairs.

If you use multiple services to send email (e.g., CRM and newsletter tools), each should have its own DKIM selector.

For more details on DKIM, read this blog 👉 What is DKIM Record: Definitive Guide [2025]

DMARC (Domain-based Message Authentication, Reporting, and Conformance)

DMARC sits on top of SPF and DKIM, which specify how receiving servers should handle messages that are not authenticated. It also sends reports so domain owners can see who’s sending on their behalf.

The DMARC requirements by Microsoft for Outlook are as follows:

• Microsoft requires a minimum policy of p=none, with alignment to either SPF or DKIM (preferably both).
• Over time, senders are encouraged to move to stricter settings, such as “quarantine” or “reject.”
• Alignment means the “From” domain must match the domain used in SPF or DKIM.

DMARC reports (RUA) are valuable for monitoring who is sending on your behalf. Microsoft sends these if requested in your DMARC record.

Pro Tip: For your DMARC policy, start with “none,” monitor reports via “rua” tags, and gradually move toward stricter policies.

Email Hygiene Best Practices Recommended by Outlook

Even if you pass SPF, DKIM, and DMARC checks, poor email hygiene can still land you in trouble. Microsoft strongly advises the following:

✔️ Valid Sender Addresses

• Your “From” or “Reply-To” email should be an actively monitored address.
• Avoid using no-reply addresses that prevent user feedback.

✔️ Functional Unsubscribe Links

• Include a clearly visible opt-out link in all marketing emails.
• A working unsubscribe mechanism is legally required in many regions and improves recipient trust.

✔️ Maintain List Hygiene

• Regularly scrub your mailing list to remove invalid or inactive addresses.
• A bounce rate above 2% is considered problematic.

✔️ Transparent Content Practices

• Subject lines should reflect the email’s actual content.
• Avoid deceptive headers or bait-and-switch tactics.

According to Validity’s 2023 Email Benchmark Report, marketers with poor list hygiene saw a 27% higher spam complaint rate and 34% lower deliverability.

Enforcement Timeline and Phases

Here’s how these new requirements will roll out:

• May 5, 2025: Soft enforcement begins. Emails from high-volume domains that fail SPF, DKIM, or DMARC will be directed to the Junk/Spam folder.
• Future Date (TBD): Later in 2025, full enforcement will take effect. Anyone who fails to authenticate their emails may be blocked entirely.

This phased approach gives senders a grace period to align their configurations. Don’t wait until messages vanish into the void.

If you don’t know how to set up SPF, DKIM, and DMARC in your DNS settings, feel free to contact us. Our team of technical media specialists is here to help. Click here to Book a Call Now! 

How to Stay Compliant with Microsoft Outlook’s New Rules

Let’s dive into the action plan. Here’s how you can adapt and thrive under the new sender policies:

Step #1: Authenticate All Emails

Double-check your SPF, DKIM, and DMARC records for all sending domains. Use tools like:

• MXToolbox
• DMARC Analyzer
• Google’s CheckMX tool
• Spam Score Checker by Post SMTP

Pro Tip: Use a p=quarantine or p=reject DMARC policy if your authentication setup is solid. Microsoft may favor stricter policies for high-volume senders.

Step #2: Align Your Domains

Make sure your “From” address domain aligns with your SPF and DKIM domains. If you’re using third-party services like Mailchimp, SendGrid, Brevo, Mailgun or Postmark—verify that your custom domain is authenticated properly.

Step #3: Monitor Spam Complaint Rates

Actively monitor your complaint rates through:

• Microsoft SNDS (Smart Network Data Services)
• Feedback loops (FBLs) with major mailbox providers
• Your ESP (Email Service Provider) dashboards

According to Validity’s 2024 Email Benchmark Report, the average spam complaint rate for reputable senders is around 0.07%.

Microsoft has not specified any specific rate yet, but Google and Yahoo start throttling or blocking traffic if your complaint rate consistently exceeds 0.3%. Therefore, make sure your spam rate remains below 0.1%.

Step #4: Review Your Reverse DNS Records

Match your sending IP’s rDNS with your sending domain. This is often overlooked but critically important. Many ESPs handle this automatically, but if you manage your own mail servers, make it a priority to do so.

Step #5: Maintain a Clean Mailing List

Use confirmed opt-ins and regularly purge inactive or bouncing emails. Focus on engaged users, not the size of the list.

Remember that email lists with high engagement rates experience higher inbox placement than those with inflated, outdated lists.

That’s all you need to know about the new Microsoft Outlook’s sender requirements.

Need Help for Setting Up SPF, DKIM, and DMARC Records?

We understand that getting your domain fully authenticated can feel overwhelming, especially with all the technical details involved—but you don’t have to figure it out alone. Our team of experienced email specialists is here to help.

Whether you’re struggling with SPF syntax, unsure how to generate DKIM keys, or need guidance crafting a solid DMARC policy, we offer hands-on support to get everything set up correctly. We’ll work directly with your DNS provider and email platform to ensure your records are configured the right way from the start.

Ready to boost your deliverability and protect your domain? Contact us today to get expert help from our technical team.

FAQs Answered by Microsoft (With Clarification)