Sending to Microsoft - What's Changed?

As of May 5, 2025, Microsoft has started actively rejecting emails from high-volume senders that don’t meet their new authentication requirements. This aligns with recent moves from Google and Yahoo, making these standards the new norm across inbox providers.

If you’re sending more than 5,000 emails per day to Microsoft consumer domains (like @outlook.com, @hotmail.com, @live.com), you must comply — or your emails may bounce completely.

🔐 New Required Standards

1. SPF (Sender Policy Framework)

• Your domain's DNS must list the IP addresses allowed to send emails.
• Microsoft will enforce alignment — the domain in the Return-Path should match your "From" or authenticated domain.

2. DKIM (DomainKeys Identified Mail)

• You need to cryptographically sign your emails.
• Microsoft recommends using aligned DKIM, where the signing domain matches your "From" domain.

3. DMARC (Domain-based Message Authentication, Reporting & Conformance)

• Required with at least a p=none policy.
• DMARC alignment must pass with either SPF or DKIM — preferably both.
• Without it? Expect this error:
• 550 5.7.515 Access denied, sending domain does not meet the required authentication level.

🧼 Microsoft's Additional Recommendations (Not technically mandatory — but practically, yes)

• ✅ Valid 'From' and 'Reply-To' addresses
• Ensure they’re monitored and functional.
• 🧼 Clean your lists
• Regularly remove hard bounces, spam traps, and unengaged users.
• 🔗 Functional unsubscribe links
• Microsoft now looks closely at how easy it is to opt out — both technically and UX-wise.
• 🧠 Send relevant content only to opted-in users
• Consent is increasingly being scrutinized.
• ⚠️ Avoid misleading subject lines, reply manipulation, or header spoofing

📉 What Happens If You Don’t Comply?

Short-term:

• Emails get bounced outright or diverted to spam.
• Engagement drops — which impacts sender reputation.

Long-term:

• IP/domain reputation gets torpedoed.
• Recovery becomes expensive (think consultants, tooling, rewarming).
• You might get blacklisted across Microsoft infrastructure.

🛠 What To Do Now (If You Haven’t Already)

✅ Run an Authentication Audit:

• Use tools like MxToolbox, Google Postmaster Tools, or a platform like Mailyser 😉 to check your SPF, DKIM, and DMARC setup.

🕵️ Monitor for Microsoft-specific errors:

• Keep an eye on SMTP response codes.
• The 550 5.7.515 error is the key flag for these new enforcement policies.

🧪 Consider DMARC enforcement (move to p=quarantine or p=reject):

• Especially important for preventing spoofing and phishing.

📬 Use BIMI if possible:

• While not enforced by Microsoft, adding BIMI (Brand Indicators for Message Identification) signals trust and can improve open rates.

💡 Why This Matters

Email deliverability is no longer just a technical issue — it’s a brand issue. Your ability to land in the inbox affects customer trust, revenue, and long-term marketing performance.

This isn't just about spam filters. It's about protecting your domain.

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