TL;DR

Starting May 5, 2025, Microsoft officially began enforcing new requirements for bulk email senders targeting consumer domains like outlook.com, hotmail.com, and live.com. If you send 5,000+ emails per day to these domains, this is your wake-up call to get compliant—or risk having your emails blocked.

📌 Why This Matters

After Gmail and Yahoo rolled out their bulk sender policies in 2024, Apple followed suit with strict privacy-first requirements in early 2025. Now, Microsoft has joined the club with its own rules focused on improving inbox quality, security, and user trust.

If you’re already following best practices, you’re likely 80% there. But Microsoft has its quirks—so here’s what you need to review and adjust today.

🧑‍💻 Does This Apply to You?

If you send:

• Newsletters
• Promotional emails
• Product launches
• Non-triggered campaigns

AND you’re sending 5,000+ messages per day to Microsoft consumer domains, you must comply.

Even if you send less, following these rules future-proofs your deliverability.

🚨 What Microsoft Requires

✅ 1. Proper Email Authentication: SPF, DKIM, and DMARC

These aren’t suggestions—they’re mandatory. Microsoft will reject unauthenticated emails with errors like:

550 5.7.515 Access denied, sending domain [yourdomain.com] does not meet the required authentication level.

Action Items:

• Publish valid SPF records
• Enable DKIM signing
• Set up a DMARC policy (start with p=none and monitor)

Pro tip: Use tools like MxToolbox or EasyDMARC to verify your setup.

🧵 2. Include a Functional, Easy-to-Find Unsubscribe

Every email must include:

• A clear unsubscribe link in the body
• List-Unsubscribe headers in the email metadata

To be compliant with Microsoft’s expectations, support both GET and POST unsubscribe requests. This is increasingly seen as a minimum standard.

List-Unsubscribe: https://yourdomain.com/unsubscribe List-Unsubscribe-Post: List-Unsubscribe=One-Click

Tip: Return 200 OK for POST requests and show a standard unsubscribe page for GETs.

📉 3. Keep Spam Complaint Rates Below 0.3%

Yes, that’s the same threshold as Gmail and Yahoo. Microsoft wants senders who respect inboxes—and punishes those who don’t.

How to stay under 0.3%:

• Use double opt-in (where possible)
• Prune disengaged users
• Segment aggressively
• Monitor complaints daily

✉️ 4. Use Valid “From” and “Reply-To” Addresses

You can’t send from no-reply@yourdomain.com if that address doesn’t exist.

At least one of your headers (From or Reply-To) must be a functioning inbox that accepts messages (even if automated).

🛠 How to Get Compliant — Fast

If you’re using platforms like Resend, Klaviyo, SendGrid, or Postmark, most of these features are built-in or easily configurable.

Double-check:

• Domain authentication (SPF, DKIM, DMARC)
• Unsubscribe link rendering
• List-Unsubscribe headers
• Complaint monitoring

💬 Final Thoughts

Microsoft’s move is part of a larger shift toward accountability in email. As more providers push for authenticated, user-friendly messages, the inbox is becoming a better place—for both marketers and recipients.

Treat May 5, 2025, not as a headache, but as a deliverability checkpoint.

Because if your emails don’t make it to the inbox… what’s the point?