A new IP address is like a new credit history - you start with no reputation, and ISPs are cautious about mail from unknown senders. IP warmup is the process of gradually building that reputation by sending increasing volumes of email to engaged recipients over time.
Rush the warmup, and you trigger spam filters. Take too long, and you delay your email program unnecessarily. This guide covers how to warm up IPs effectively.
Why IP Warmup Matters
The Cold IP Problem
ISPs have never seen email from your new IP before. They have no data on whether you are a legitimate sender or a spammer. Their default response is caution - limiting or filtering your mail until you prove trustworthy.
What ISPs Watch During Warmup
- Volume patterns: Sudden high volume from new IP = suspicious
- Bounce rates: High bounces = bad list quality
- Complaint rates: Spam reports = unwanted mail
- Engagement: Opens and clicks = wanted mail
- Authentication: SPF, DKIM, DMARC = legitimate sender
Consequences of Poor Warmup
- Throttling or blocking by ISPs
- Poor inbox placement during and after warmup
- Longer time to full sending capacity
- Potential blocklisting
- Having to start over with a new IP
Warmup Fundamentals
Start with Your Best Recipients
Send to your most engaged users first. They are most likely to open, click, not complain, have valid addresses, and be at major ISPs (Gmail, Outlook, Yahoo).
Engagement signals during warmup are critical. Let your best users establish your reputation.
Gradual Volume Increase
Increase volume slowly. A common approach is to double volume every 2-3 days. Start with 50-100 emails per day and scale to your target volume over 4-6 weeks.
ISP Distribution
Spread sends across ISPs from the start. Do not warm up on Gmail only, then suddenly blast Yahoo. Each ISP builds reputation separately.
Consistent Patterns
Send at consistent times, maintain steady growth, avoid volume spikes or drops, and keep content quality consistent.
Warmup Schedule Example
Week 1: Foundation
- Day 1: 50 emails to most engaged users
- Day 2: 100 emails
- Day 3: 200 emails
- Day 4: 400 emails
- Day 5: 800 emails
- Day 6-7: 1,000-1,500 emails
Week 2: Building
- 2,000 to 5,000 emails per day
- Continue with engaged recipients
- Monitor for issues
Week 3-4: Accelerating
- 5,000 to 20,000 emails per day
- Gradually include less engaged users
- Watch ISP-specific metrics
Week 5-6: Full Capacity
- Ramp to target volume
- Full list included
- Continue monitoring
Adjusting the Schedule
This is a guideline, not a rule. Slow down if you see high bounces, complaints, blocks, or poor engagement. Speed up if metrics are excellent and ISPs are not pushing back.
Monitoring During Warmup
Critical Metrics
- Bounce rate: Should stay under 2%, ideally under 1%
- Complaint rate: Must stay under 0.1%
- Open rate: Should be high (sending to engaged users)
- Delivery rate: Watch for throttling (4xx responses)
ISP-Specific Monitoring
Track delivery by ISP. Gmail, Outlook, and Yahoo may behave differently. Use Google Postmaster Tools for Gmail visibility.
Red Flags
- Sudden increase in deferrals or blocks
- Spam folder placement increasing
- Complaint rate spiking
- Bounce rate climbing
When to Pause
If you see serious issues, pause sending rather than push through. Investigate the cause. Fix the problem. Resume slowly.
Warmup Best Practices
Authentication First
Have SPF, DKIM, and DMARC properly configured before starting. Authentication issues during warmup damage reputation when it matters most.
Clean Lists
Validate your list before warmup. Remove known bounces and complainers. High bounces during warmup are devastating.
Quality Content
Send your best content during warmup. Engagement matters more during warmup than at any other time.
Segment Strategically
Segment your most engaged users for warmup. Sort by recent opens, clicks, or purchases. These are your warmup champions.
Multiple IPs
If warming multiple IPs, do not warm them all identically. Stagger starts, slightly vary schedules, and monitor each separately.
Common Warmup Mistakes
Starting Too Aggressively
Sending thousands of emails on day one guarantees problems. Start small.
Using Cold Lists
Lists that have not been mailed recently are risky. Many addresses may be invalid or abandoned. Consider re-engagement campaigns on warm IPs first.
Ignoring Warning Signs
High deferrals are the ISP telling you to slow down. Listen to them.
Inconsistent Sending
Sending nothing for days, then blasting volume, looks suspicious. Maintain consistency.
Stopping Too Early
Reputation takes time to solidify. Do not consider warmup complete after one good week. Full warmup is typically 4-6 weeks.
Maintaining Post-Warmup
Ongoing Practices
- Maintain consistent sending volume
- Continue list hygiene
- Monitor reputation metrics
- Address issues promptly
Volume Changes
If you need to significantly increase volume after warmup, ramp gradually rather than jumping. Treat major increases as mini-warmups.
Conclusion
IP warmup requires patience and attention. The reward is a strong sender reputation that supports reliable delivery at full volume. Rush it, and you create problems that take months to resolve.
Invest the 4-6 weeks in proper warmup. Your future email program depends on it.
GetMailer provides dedicated IP addresses with guided warmup programs. Our platform monitors warmup metrics automatically and alerts you to issues before they become problems.