A brand-new domain or IP has no sending history. Mailbox providers treat unknown senders with extreme caution by default. If your first action from a new domain is sending 10,000 cold emails, you will land in spam and stay there for months. The fix is a deliberate four-week warm-up that builds trust gradually.
What warm-up actually does
Warm-up is the process of slowly increasing send volume from a new domain while engineering high engagement signals (opens, clicks, replies). Mailbox providers watch the volume curve and the engagement curve together. A new sender showing healthy ramp and strong engagement gets trusted quickly. A new sender showing sudden volume with low engagement gets demoted to spam permanently.
The 4-week warm-up schedule
| Day | Emails/day | Engagement target |
|---|---|---|
| 1-3 | 5 | 100% open, 80% reply |
| 4-6 | 10 | 90% open, 60% reply |
| 7-9 | 20 | 80% open, 40% reply |
| 10-12 | 40 | 70% open, 30% reply |
| 13-15 | 80 | 60% open, 20% reply |
| 16-21 | 150 | 50% open, 10% reply |
| 22-28 | 300 | 40% open, 5% reply |
By day 28 you are sending 300 per day with healthy engagement. From here you can scale to your actual campaign volume over another 2 to 4 weeks.
How to engineer engagement during warm-up
You cannot just send to a cold list and hope for opens. You need engagement. Three options:
- Use a warm-up tool. Lemwarm, Mailwarm, Warmup Inbox automate the process. Your inbox sends to other warm-up participants, who reply and engage automatically. Costs $20 to $50 per month per inbox. Worth it.
- Email your existing engaged list first. If you have a healthy list on another domain, send first to your top 20% openers from the new domain. Real engagement, no fake automation.
- Internal warm-up. Send to coworkers, friends, family, and ask them to open, reply, mark as Important. Slow and labor-intensive but free.
Authentication before warm-up
None of this works without proper authentication. Before day 1:
- SPF record published and passing.
- DKIM keys set up and passing.
- DMARC record at
p=nonefor the first 30 days, then move top=quarantine. - Custom return-path domain configured.
- BIMI (optional but helpful for trust).
Monitoring during warm-up
Check daily:
- Google Postmaster Tools: domain reputation should move from "Unknown" to "Low" by day 7, "Medium" by day 21.
- Bounce rate: must stay under 2%.
- Complaint rate: must stay under 0.1%.
- Inbox placement (use Gmail Mail Tester or Glock Apps).
What kills a warm-up
- Sending to invalid addresses. Pre-verify every list before sending. A 5% bounce rate on day 5 destroys the warm-up.
- Volume spike. Going from 40 to 4,000 in one day looks like a botnet.
- Bad content. Aggressive subject lines, all-image emails, low engagement messages.
- Sending only on weekdays then suddenly weekends. Pattern shifts are red flags. Keep send rhythm consistent.
Warming a brand-new IP
If you also have a dedicated IP (not a shared ESP IP), warm it in parallel. The volume schedule is identical. Some senders use a "primary domain on shared IP, secondary domain on dedicated IP" pattern to isolate cold-email risk.
FAQ
Can I skip warm-up by buying a "warm" domain?
Aged domains exist but are expensive and risky. Most have unknown sending history. Cheaper and safer to warm a fresh domain yourself.
What if my domain reputation drops mid-warmup?
Pause. Investigate. Almost always the cause is bounce rate or low engagement. Fix the list, restart at the previous day's volume, ramp again.
How long until I can send 10,000+ per day?
Six to ten weeks from a cold start, assuming everything goes right. Plan accordingly.
Foundation step: verify your warm-up list
Bounces during warm-up are the most common cause of failed reputation building. Verify every list before send.