What to do when Microsoft throttles but Gmail is fine?
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Your mail to Gmail moves instantly. Your mail to Outlook and Hotmail lands 30 minutes later, if at all. That's throttling. Microsoft has decided you're suspicious, even if Gmail is happy. The good news: this is usually fixable. The bad news: it's specific to Microsoft's reputation system, not a general deliverability problem.
Check your IP reputation through SNDS. Microsoft publishes the Sender Network Data Service (SNDS), which shows your IP's health from Microsoft's perspective. Log in and check your status. Is your IP listed as green (good), yellow (flagged), or red (blocked)? Look at the trap hit data. Trap hits are emails sent to addresses that were never subscribed to but are still active. Too many traps signal a bad list source. Check your complaint rate as seen by Microsoft. Microsoft is more sensitive to complaints than Gmail. A 0.3% complaint rate might be fine for Gmail but trigger throttling at Microsoft.
Understand why Microsoft is stricter than Gmail. Gmail uses content analysis and machine learning to filter mail. Microsoft relies more heavily on sender reputation (IP-based). If your IP has history, Microsoft penalizes harder. Gmail also whitelist senders it recognizes. Microsoft is slower to build trust. Additionally, Microsoft's SmartScreen filter applies rules based on complaint patterns and engagement signals.
How to fix it. Reduce your volume to Microsoft domains by 25 to 50% for a few days. This gives Microsoft a chance to rebuild trust without you hammering them. At the same time, audit your list. Are you sending to addresses that have never engaged? Clean them aggressively. Run a validation check on your sending addresses to identify trap hits and catch-alls. Verify your SPF, DKIM, and DMARC records are passing consistently. Check with MxToolbox to confirm your records are correct.
Once you've cleaned the list and verified authentication, request mitigation through the SNDS dashboard. Microsoft will review your changes. If you're showing improvement, they'll lift the throttle within 24 to 72 hours.
Your next step: log into the SNDS dashboard today. Take a screenshot of your status and complaint data. Then check your list import logs for the past 30 days. Are there any imports you don't recognize or that came from questionable sources?
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