📢 Microsoft to Block Unauthenticated Emails Starting May 5, 2025 — What You Need to Know
- Adam Corder
- May 21
- 1 min read
🛑 New Enforcement: Email Rejections with “550 5.7.15 Access Denied”
Beginning May 5, 2025, Microsoft will block emails that fail authentication standards—no longer simply sending them to spam. Instead, emails that don’t meet the requirements will be rejected outright with this error:
550 5.7.15 Access denied, sending domain [SendingDomain] does not meet the required authentication level.
👥 Who Is Affected?
This change impacts high-volume senders—any domain sending 5,000+ emails per day to these Microsoft domains:
🔒 Required Email Authentication Protocols
To stay compliant and avoid rejection, your domain must pass all three of the following:
Requirement | Purpose | |
SPF | Valid DNS record listing authorized IPs | Prevents spoofing |
DKIM | Cryptographic signature in email header | Ensures message integrity |
DMARC | Policy set to at least p=none, with alignment | Controls how to handle failed SPF/DKIM |
⚠️ Common Causes of the 550 5.7.15 Error
Administrators may encounter this error due to:
Missing or misconfigured SPF, DKIM, or DMARC
Domain misalignment between “From” address and auth records
SPF DNS lookup limit exceeded (10 maximum)
Third-party services (e.g., Mailchimp, Salesforce) not properly authenticated
🛠️ What to Do Now
Take proactive steps to ensure deliverability before enforcement begins:
✅ Audit your domain’s email authentication
✅ Use specialized DMARC analysis tools, not just DNS checkers
✅ Coordinate with email service providers (ESPs)
✅ Monitor using analytics dashboards
✅ Get Compliant. Stay Delivered.
Don’t wait until your emails start bouncing. If your business relies on email for communication, sales, or customer engagement, now is the time to act.
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