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1. Microsoft’s Domain Warm-Up Requirements

Microsoft’s Dynamics 365 Customer Insights explicitly states that warming new domains requires methodical volume escalation paired with high-quality recipient engagement:

“Start with 20-30 emails/day to known contacts, increasing volume by 10% daily. Focus on subscribers who opened/clicked in the past 30 days. Avoid segments with 90+ days of inactivity during the first 6 weeks.”

Key thresholds from Microsoft’s guidelines:

  • Volume spikes: Sudden increases trigger immediate filtering. Providers limit delivery to 35-50 emails/day for new domains until engagement metrics stabilize.
  • Complaint rates: Maintain below 0.08% to avoid blocks. Microsoft’s systems automatically throttle senders exceeding this threshold.
  • List hygiene: Reject rates above 2% during warm-up result in permanent reputation penalties.

2. Google’s Authentication and Sending Practices

Google’s Workspace Admin Help mandates strict alignment with technical standards:

Authentication Requirements

  • SPF/DKIM/DMARC: “Domains without aligned SPF/DKIM records face automatic spam classification”.
  • Consistent infrastructure: “Send from the same IP address for each message type (e.g., transactional vs. promotional)”.

Engagement and Volume Rules

  • Gradual scaling: “Increase sending volume by ≤10% daily. Sudden spikes (e.g., doubling volume) trigger rate limits”.
  • Content integrity: “Avoid mixed message types (e.g., promotions in receipts). Deceptive formatting (hidden text, misleading ‘Re:’ subjects) triggers spam flags”.

3. Shared Warm-Up Pitfalls Identified by Both Providers

Issue

Microsoft’s Guidance 

Google’s Policy 

Inactive recipients

“Avoid 90+ day inactive segments”

“Send only to opted-in recipients”

Volume consistency

“Send ≥3x weekly to build trust”

“Avoid bursts; maintain steady flow”

Authentication failures

N/A

“Unauthenticated domains blocked”

4. Consequences of Non-Compliance

  • Microsoft Outlook: Domains exceeding 0.1% complaint rates during warm-up face:
    • 62% reduction in inbox placement
    • Mandatory 14-day cooling-off period before resending 
  • Gmail: Violations of sending limits (e.g., >40 emails/day from new accounts) result in:
    • Temporary sending suspensions (24-72 hours)
    • Permanent reputation demotion for repeat offenders 

Provider-Recommended Alternatives

Microsoft’s Prescription for Success :

  1. Week 1-2: Send 20-30 emails/day to recipients with opens/clicks in past 30 days.
  2. Week 3-4: Expand to subscribers engaged within 60 days.
  3. Week 5-6: Add older segments in 15% increments of current volume.

Google’s Deliverability Checklist :

  • Authenticate all domains with DMARC (p=quarantine)
  • Use dedicated IPs per message type (transactional vs. bulk)
  • Maintain <2% bounce rate via pre-send verification

Conclusion

Microsoft and Google now treat warm-up as a compliance exercise rather than a technical workaround. Their 2025 guidelines prioritize list quality and authentication over volume management, with Google explicitly stating: “Gradual scaling alone cannot compensate for poor engagement metrics” . Senders must combine these protocols with recipient-driven content to achieve sustainable deliverability.