Case Study: How We Warmed Up a Fresh Domain to 98% Inbox Rate

We launched a brand new domain on December 1, 2025. No sending history. No reputation. Cold start.

By December 30, we hit 98% inbox rate with consistent reply rates above 3%. This is the exact day-by-day breakdown.

This case study follows the methodology in our Cold Email Infrastructure Guide. For the architectural philosophy, read our SaaS Infrastructure Guide.

Starting Point: Domain Zero State

Domain: outreach.pipecrush.io (subdomain of our main domain) Registration date: December 1, 2025 IP address: Dedicated, clean reputation Goal: 90%+ inbox rate within 30 days

Why a Subdomain Instead of New Root Domain?

Subdomain advantages:

• Inherits some trust from parent domain
• DNS records already established
• Faster warm-up compared to brand new domain

Trade-off: Subdomains warm up 40% faster, but if you burn the subdomain, it can hurt your parent domain.

Pre-Launch: Infrastructure Setup (Days -7 to 0)

Day -7: DNS Configuration

SPF Record: v=spf1 include:_spf.pipecrush.io include:amazonses.com ~all

DKIM Keys: 2048-bit RSA, published in DNS

DMARC Policy: v=DMARC1; p=none; rua=mailto:dmarc@pipecrush.io; fo=1; pct=100

Day -3: IP Warm-up Strategy

Warm-up schedule designed:

• Days 1-7: 20-50 emails/day
• Days 8-14: 100-200 emails/day
• Days 15-21: 300-500 emails/day
• Days 22-30: 1,000-2,000 emails/day

Target recipients for Phase 1: Internal team members, opted-in customers, known partners.

Days 1-7: Foundation Phase

Day 1: First Sends (20 emails)

Recipients: 10 internal team + 10 engaged customers Results: 100% delivered, 90% opened, 60% replied, 100% inbox rate

Day 7: End of Week 1 (50 emails/day)

Results: 96% inbox rate (2 emails landed in spam for cold prospects)

Week 1 Totals: 240 emails, 0% bounce rate, 98% average inbox rate

Days 8-14: Scaling Phase

Day 14: End of Week 2 (200 emails/day)

Results: 93% inbox rate

Week 2 Totals: 1,050 emails, 0.8% bounce rate, 0.05% complaint rate

Key learning: First spam complaint came from cold prospect. Reviewed list source and tightened targeting.

Days 15-21: Optimization Phase

Day 18: Alert Triggered

Inbox rate dropped below 90% threshold.

Root cause analysis:

• Gmail: 92% inbox (fine)
• Outlook: 78% inbox (problem area)

Hypothesis: Outlook has stricter filters for new senders.

Fix: Reduced Outlook sends temporarily while maintaining Gmail volume.

Day 21: End of Week 3

Week 3 Totals: 2,800 emails, 1.2% bounce rate, 91.3% average inbox rate

Trend: Outlook reputation improving.

Days 22-30: Full Production

Day 30: Final Test (2,000 emails/day, 100% cold)

Results:

• Delivered: 98.2%
• Opened: 53%
• Replied: 7%
• Inbox rate: 98%

30-Day Summary: The Numbers

Metric	Result	Target	Status
Final inbox rate	98%	90%	Exceeded
Average inbox rate	94.2%	85%	Exceeded
Total emails sent	15,590	—	—
Bounce rate	1.1%	<3%	Passed
Complaint rate	0.07%	<0.3%	Passed
Reply rate	7.2%	>2%	Exceeded

Lessons Learned

1. Start with Warm Audiences

Gmail and Outlook watch early engagement signals closely. High engagement in Days 1-7 set the trajectory for success.

2. Gradual Volume Increases

ESPs see natural growth pattern. Sudden spikes trigger spam filters.

3. Real-Time Monitoring and Adjustments

When Outlook dropped to 78%, we reduced volume and let reputation recover. Monitoring isn't passive.

4. Content Quality Matters

Best performing template:

Subject: Quick question about [Company]'s [pain point]

Hi [First Name],

I noticed [specific observation about their company].

We help [similar companies] solve [specific problem].

Worth a 10-minute call to explore?

Reply rate: 8.2% (vs. 4.1% for generic templates)

5. List Quality Trumps List Size

$50 spent on list verification saved us from 500+ bounces.

Replicable Framework

Week 1: 20-50 emails/day to warm audiences. Goal: 95%+ inbox rate.

Week 2: 100-200 emails/day, introduce cold prospects gradually. Goal: Maintain 90%+.

Week 3: 300-500 emails/day, monitor ESP-specific performance. Goal: Fix weak points.

Week 4: 1,000-2,000 emails/day, full cold prospect volume. Goal: Maintain 90%+.

Platform Requirements

This case study used:

• Dedicated IP (included in our email marketing platform)
• Custom DKIM/SPF/DMARC
• Real-time deliverability monitoring
• Automated bounce handling
• AI sequences for follow-up automation

The Bottom Line

A brand new domain can reach 98% inbox rate in 30 days—if you have the right infrastructure and follow a disciplined warm-up process.

The three pillars:

1. Infrastructure: Dedicated IP, proper DNS authentication, monitoring
2. Process: Gradual volume increases, engagement-first targeting
3. Content: Personalized, relevant, valuable emails

This wasn't luck. It's repeatable engineering.

For the complete technical setup guide, read our Cold Email Infrastructure Guide. And if you want infrastructure that includes everything we used in this case study, try our CRM and email marketing platform.

Frequently Asked Questions

What's the biggest mistake in domain warmup?

Rushing. New senders want to blast 1,000 emails immediately. Inbox providers flag sudden volume spikes as spam behavior. Proper warmup means starting with 10-20 emails/day and increasing by 20-30% weekly over 4-6 weeks. There's no shortcut—attempting one destroys the domain you're trying to build.

Can I warm up multiple domains simultaneously?

Yes, and you should if you're planning high-volume outreach. Warm up 5-10 domains in parallel so you have capacity when you need it. Each domain needs its own warmup sequence—you can't transfer reputation between domains. Plan 6-8 weeks ahead of when you need full sending capacity.

What should I send during warmup?

Real emails to real people who will engage. Best approach: reach out to existing contacts, partners, or warm prospects who are likely to open and reply. Automated warmup tools simulate engagement, but real engagement is better. Mix promotional and conversational emails to establish normal sending patterns.

How do I know if warmup is working?

Monitor: inbox placement (use seed testing), open rates (should be 40%+ during warmup), bounce rates (under 2%), spam complaints (under 0.1%). Check Google Postmaster Tools for domain reputation—should show "Good" or "High" within 3-4 weeks. If metrics decline, slow down immediately.

What kills a domain during warmup?

Fatal mistakes: (1) Sending to purchased lists with high bounce rates, (2) Increasing volume too quickly, (3) Sending identical content to many recipients, (4) Ignoring spam complaints, (5) Not having SPF/DKIM/DMARC configured before starting. Any of these can permanently damage domain reputation.

Can I recover a domain with damaged reputation?

Sometimes, but it takes longer than starting fresh. Stop all sending for 2-4 weeks. Fix whatever caused the damage. Restart warmup from zero—even slower than original. If reputation doesn't recover within 8 weeks, the domain may be permanently flagged. Prevention is far easier than recovery. Learn proper email infrastructure.