You just bought a shiny new domain. Set up your ESP. Imported your list of 10,000 contacts. Time to blast your first campaign and watch the money roll in.
Nope.
You just torpedoed your sender reputation before you even got started. Gmail saw a brand new domain suddenly sending thousands of emails and flagged you as spam. Your sender reputation was toast before you even started faster than you can say "but I'm a legitimate business."
Email warmup is the difference between landing in the inbox and getting blacklisted by every major provider on the planet.
What Email Warmup Actually Is
Email warmup is the process of gradually increasing your sending volume from a new or dormant email account to build trust with inbox providers. Skip it and you'll spend three months wondering why your open rates are at 4%. You're basically proving to Gmail, Outlook, and Yahoo that you're a real sender, not some spammer who bought a domain an hour ago.
When you warm up properly:
- Inbox providers see consistent, positive engagement
- Your sender reputation builds over time
- Your emails land in Primary, not spam
- You avoid getting blacklisted before you start
When you skip warmup:
- Providers flag you as suspicious
- Your first campaign goes straight to spam
- Your domain gets a bad reputation from day one
- Good luck fixing that for the next six months
According to Omnisend, a good email deliverability rate is above 85%, while excellent falls at 95% or higher. Skip the warmup and you'll be lucky to hit 40%.
Why Inbox Providers Are So Paranoid
Gmail processes over 300 billion emails per year. Most of it is spam. Their entire job is protecting users from garbage, and they're really good at it.
When a new domain appears out of nowhere and starts sending volume, every alarm bell goes off. No history. No reputation. No trust. You're guilty until proven innocent.
The warmup period is you proving innocence. You're saying "look, I send emails, people open them, people click them, nobody marks me as spam." Do that consistently for 4-8 weeks and providers start trusting you.
Skip it? You're just another spammer in a sea of spammers.
The 4-Week Warmup Schedule That Works
Stop overthinking this. Here's the exact schedule.
| Week | Daily Volume | Focus |
|---|---|---|
| 1 | 20-50 emails | Your most engaged subscribers only |
| 2 | 50-100 emails | Engaged subscribers, monitor metrics |
| 3 | 100-250 emails | Expand to warm subscribers |
| 4+ | 250-500 emails | Gradual increase, watch deliverability |
A few rules:
Week 1 is critical. Only send to people who will definitely open. Your best customers. People who signed up yesterday. Anyone with high engagement history.
Watch your metrics obsessively. If open rates drop or spam complaints appear, slow down immediately.
Don't send to cold subscribers until week 5 or 6 at the earliest. They're the ones who tank your metrics.
After week 4, you can gradually scale up. But "gradually" means 10-20% increases, not doubling overnight.
Manual Warmup vs Automated Tools
You've got two options.
Manual warmup means you control everything. Send to your engaged list first. Track metrics yourself. Adjust volume based on what you see.
Pros: Free. Full control. You learn your list. Cons: Time-consuming. Easy to mess up.
Automated warmup tools handle it for you. They send emails between accounts in their network to simulate engagement and build your reputation.
Pros: Hands-off. Consistent. Faster in some cases. Cons: Costs money. Some providers hate synthetic engagement.
| Method | Best For | Risk Level |
|---|---|---|
| Manual to real subscribers | Marketing emails, newsletters | Low |
| Automated tools | Cold outreach, sales emails | Medium |
| No warmup at all | Nobody. Ever. | Catastrophic |
For most email marketers, manual warmup to real subscribers is the move. Your engaged subscribers are going to open your emails anyway. Use them.
Automated tools work better for cold outreach where you don't have an engaged audience to start with.
Signs Your Warmup Is Working
You're looking for these signals:
Open rates above 30% in the first two weeks. If people aren't opening, providers notice.
Zero spam complaints. One complaint per 1,000 emails is bad. Multiple complaints? Stop and reassess.
Low bounce rates. Under 2% is good. Higher means your list is garbage or you're hitting spam traps. Time for some list hygiene. Also make sure your authentication is set up correctly.
Gmail Postmaster Tools showing "good" reputation. Set this up on day one. It's free and tells you exactly what Google thinks of your domain.
If your metrics look healthy after 4 weeks, you're ready to scale.
Signs Your Warmup Is Failing
Bad news comes in several flavors.
Open rates tanking week over week. Started at 40%, now at 15%? Something went wrong. Probably sending to the wrong segments too fast.
Bounce rates climbing. This means you're hitting invalid addresses or spam traps. Clean your list immediately.
Emails landing in spam. Check with seed accounts. If Gmail is filtering you, slow everything down.
Blacklist warnings. Use a tool like MXToolbox to check if your domain landed on any blacklists. If it did, stop all sending and fix the problem before continuing.
Common Warmup Mistakes
I've seen all of these. Multiple times.
Sending to your entire list on day one. You're not special. Gmail doesn't care that you're a "legitimate business." Neither does Outlook. Start small.
Importing old, unengaged lists. That list of 50,000 emails you bought three years ago? Delete it. Or at least validate it before touching it.
Inconsistent sending patterns. Sending 50 emails on Monday, nothing for two weeks, then 500 on a Friday. Providers notice. Be consistent.
Ignoring engagement. If people aren't opening, stop sending to them. Include them later or not at all.
Rushing through warmup. Four weeks minimum. Eight is better for high-volume senders. There are no shortcuts that don't come back to bite you.
What Happens If You Skip Warmup
You send 5,000 emails from your brand new domain. Gmail sees a new sender blasting volume with no history. Red flag.
Your bounce rate hits 8% because the list is old. Another red flag.
Open rates are 12% because half the list forgot who you are. More flags.
Two people click "Report Spam" because they don't remember subscribing. That's it. You're done.
Gmail starts routing you to spam. Your next campaign does even worse. Open rates drop to 5%. More spam complaints. Now you're on a blacklist.
Your domain reputation is destroyed. Fixing it takes months. Sometimes you have to start over with a new domain entirely.
All of this was avoidable with four weeks of patience.
FAQ
How long does email warmup take?
Minimum four weeks for low-volume senders. Eight weeks or more if you plan to send thousands of emails per day. Don't rush it.
Can I warmup an existing domain that went cold?
Yes, but treat it like a new domain. Start with engaged subscribers only and gradually rebuild trust. It might take longer than starting fresh.
Do I need to warmup if I'm using a shared IP?
Shared IPs have existing reputation, but you still need to warm up your domain. The domain reputation and IP reputation are separate. Ignore either and you'll have problems.
What's a good open rate during warmup?
Aim for 30% or higher in the first two weeks. You're sending to your most engaged subscribers so this should be achievable. If you're under 20%, something's wrong.
Should I use a warmup tool or do it manually?
For marketing emails to your own list, manual warmup works great. For cold outreach where you don't have engaged subscribers, automated tools fill the gap. Either way, warmup is not optional.