Microsoft’s May 2025 Spam Filter Update: Why Your Emails Are Getting Flagged—and What to Do About It

In May 2025, Microsoft rolled out major changes to its spam filtering system—and many organizations are feeling the impact. The update introduced stricter rules around email authentication, causing a spike in false positives (legitimate emails being marked as spam or sent to quarantine).

🔍 What Changed?

Microsoft now requires all bulk email senders to meet SPF, DKIM, and DMARC standards. If your organization sends newsletters, alerts, or transactional emails—and your authentication isn’t airtight—your messages might not make it to the inbox.

They’re also being stricter with:

• Sender reputation

• Domain alignment

• Message header validation

These changes are meant to fight phishing and spoofing, but they can also block valid messages from reaching users.

⚠️ Why Legit Emails Are Going to Spam

• Missing or misconfigured SPF/DKIM/DMARC records

• Aggressive spam settings in Microsoft Defender

• Bulk senders flagged as risky, even when legitimate

• Rapid enforcement with little transition time

✅ How to Fix It

1. Audit Email Authentication
Make sure SPF, DKIM, and DMARC records are valid and aligned with your sending domains.

2. Review Spam Filter Policies
Adjust Microsoft 365 anti-spam settings and disable overly aggressive filters if needed.

3. Use Allow/Block Lists Wisely
Temporarily allow trusted senders, but avoid whitelisting broadly—this can increase security risks.

4. Educate Users
Encourage use of the “Not Junk” button and escalate false positives to IT.

5. Clean Up Mailing Lists
Remove inactive or invalid addresses to improve sender reputation and reduce bounce rates.

🛡 Stay Ahead of Disruptions

Microsoft’s new rules improve email security—but they also require IT teams to act fast. Regular audits, smart filtering, and user training can help prevent important emails from getting lost in spam.

Need help adjusting your Microsoft 365 environment? [Book Your Free Tech Consultation]or [Call Now] to reduce false positives and keep your email flowing securely.