Outlook Enforcing Stricter Rules for Bulk Mail Senders

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As part of our ongoing commitment to keeping you informed, we wanted to share an important update regarding Outlook’s email authentication policies.

Outlook announced it was to start enforcing stricter rules for bulk mail senders (over 5,000 emails per day). These rules require full compliance with SPF, DKIM, and DMARC authentication protocols. Microsoft stated:

“For domains sending over 5,000 emails per day, Outlook will require compliance with SPF, DKIM, and DMARC. Non‐compliant messages will first be routed to Junk. If issues remain unresolved, they will eventually be rejected.”

We’ve now seen this enforcement in action.

There’s been a significant increase in emails being blocked or junked due to unaligned SPF records, even when DKIM alignment passes DMARC.

This confirms that both SPF and DKIM must align—relying on just one is no longer sufficient.


What This Means for You

If your domain sends high volumes of email and your SPF and DKIM records are not properly aligned, your messages may:

➡️ Be routed to recipients’ junk folders

➡️ Be rejected entirely by Outlook servers

➡️ Result in lost engagement and damaged sender reputation

 

What You Should Do

✅ Review all of your domains’ SPF, DKIM, and DMARC setup

✅ Ensure both SPF and DKIM are aligned for all sending sources

✅ Monitor your email deliverability and authentication reports regularly

 

If you’re unsure how to check or update your records, or if you’d like help reviewing your setup, we’re here to support you.

Let’s make sure your emails continue to land where they’re meant to—your customers’ inboxes.

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