You've set up your new email infrastructure, configured authentication, and you're ready to send. But if you blast out 100,000 emails on day one, you'll likely end up in spam—or worse, get blocklisted. Email warmup is the process of gradually building sender reputation before reaching full volume. Here's exactly how to do it.
What is Email Warmup?
Email warmup is the practice of gradually increasing your sending volume over time to establish a positive sender reputation with inbox providers. Instead of sending at full capacity immediately, you start small and scale up as ISPs learn to trust your sending patterns.
Think of it like building credit. A new credit card holder doesn't get a $50,000 limit on day one. They start small, demonstrate responsible behavior, and gradually earn higher limits. Email reputation works the same way.
Why Warmup Matters
Inbox providers like Gmail, Microsoft, and Yahoo are deeply suspicious of new senders. Their spam filters are designed to protect users from bad actors, and a brand new IP or domain sending high volumes is a red flag.
Without warmup, you'll face:
- Spam folder placement: Your emails go directly to spam, even if they're legitimate.
- Rate limiting: ISPs throttle your sending, causing delays and timeouts.
- Blocklisting: Aggressive sending can get your IP added to blocklists.
- Permanent reputation damage: First impressions matter. A bad start is hard to recover from.
The Cost of Skipping Warmup
When You Need to Warm Up
You need a warmup strategy when:
- New IP address: You've acquired a dedicated IP for sending.
- New domain: You're sending from a domain that hasn't sent email before.
- New ESP: You've switched email service providers.
- Long inactivity: You haven't sent from this IP/domain in 30+ days.
- Reputation recovery: You're rebuilding after deliverability issues.
The Warmup Schedule
A typical warmup takes 4-8 weeks depending on your target volume. Here's a proven schedule:
IP Address Warmup Schedule
For a new dedicated IP targeting 100,000 emails/day:
Week 1:
Day 1: 50 emails
Day 2: 100 emails
Day 3: 200 emails
Day 4: 400 emails
Day 5: 800 emails
Day 6: 1,500 emails
Day 7: 3,000 emails
Week 2:
Day 8: 5,000 emails
Day 9: 7,500 emails
Day 10: 10,000 emails
Day 11: 15,000 emails
Day 12: 20,000 emails
Day 13: 25,000 emails
Day 14: 30,000 emails
Week 3:
Day 15-21: 40,000 emails/day
Week 4:
Day 22-28: 60,000 emails/day
Week 5:
Day 29-35: 80,000 emails/day
Week 6+:
Day 36+: 100,000 emails/day (full volume)Domain Warmup
Domain warmup follows a similar pattern but focuses on building domain reputation rather than IP reputation. If you're using a shared IP (common with ESPs), domain warmup is your primary concern.
The schedule is similar, but you can often move faster since the IP already has established reputation. A 2-4 week warmup is typically sufficient for domain-only scenarios.
Warmup by ISP
Warmup Best Practices
1. Send to Your Most Engaged Subscribers First
During warmup, prioritize subscribers who have recently opened or clicked your emails. High engagement signals to ISPs that recipients want your mail, accelerating reputation building.
2. Maintain Consistent Sending Patterns
Send at the same time each day during warmup. Erratic patterns look suspicious. If you normally send at 10 AM, stick to 10 AM throughout the warmup period.
3. Keep Content Consistent
Don't dramatically change your email content during warmup. ISPs learn what "normal" looks like for your sending. Sudden changes can trigger filters.
4. Monitor and Adjust
Watch your metrics closely. If you see bounce rates spike or engagement drop, slow down. It's better to extend warmup than to damage your reputation.
5. Authenticate Everything
Ensure SPF, DKIM, and DMARC are properly configured before starting warmup. Authentication issues during warmup will undermine your efforts.
6. Clean Your List First
Never warm up with a dirty list. Bounces during warmup are especially damaging. Verify all addresses before your first send.
Monitoring Your Warmup Progress
Track these metrics throughout warmup:
Positive Signals (Keep Going)
- Open rates above 20%
- Click rates above 2%
- Bounce rates below 1%
- Spam complaints below 0.1%
- Inbox placement above 90%
Warning Signs (Slow Down)
- Open rates dropping significantly
- Bounce rates above 2%
- Spam complaints above 0.1%
- Emails going to spam folder
- Delivery delays or timeouts
Red Flags (Pause and Investigate)
- Bounce rates above 5%
- Blocklist notifications
- Complete delivery failures to major ISPs
- Spam complaint rates above 0.3%
Use Postmaster Tools
Common Warmup Mistakes
1. Going Too Fast
The most common mistake. Impatience leads to reputation damage. Stick to the schedule even if everything looks fine—ISPs need time to build trust.
2. Sending to Cold Lists
Warming up with subscribers who haven't engaged in months is counterproductive. Low engagement during warmup signals to ISPs that recipients don't want your mail.
3. Ignoring Weekends
Some senders pause warmup on weekends. This creates inconsistent patterns. Send every day, including weekends, even if at lower volumes.
4. Changing Too Many Variables
Don't change your email template, subject line style, and sending time all at once during warmup. Change one thing at a time so you can identify what affects performance.
5. Not Having a Backup Plan
If warmup goes wrong, you need a fallback. Keep your old sending infrastructure available until the new one is fully warmed and stable.
Conclusion
Email warmup requires patience, but it's essential for long-term deliverability success. A proper 4-6 week warmup protects your investment in email infrastructure and sets you up for sustained inbox placement.
Remember: ISPs have long memories. The reputation you build during warmup—good or bad—will follow you for months. Take the time to do it right.