Sending email from a new IP address or a new domain is one of the most common ways senders accidentally destroy their deliverability before their campaigns have even begun. A new IP has no history. Inbox providers have never seen it before. They have no way of knowing whether it belongs to a legitimate business sender or to a spammer who just spun up a fresh server to evade existing blocks.
IP warming is the process of gradually building a reputation for a new IP address or sending domain by increasing your sending volume slowly, demonstrating consistent recipient engagement, and earning the trust of inbox providers over time. Done correctly, it sets you up for long-term reliable inbox placement. Done incorrectly, or skipped entirely, it can permanently damage a domain before your real campaigns have even started.
Why Inbox Providers Care About IP Warming
Mailbox providers like Gmail, Outlook, and Yahoo use sending history as one of the most important inputs to their spam filtering decisions. When they see a consistent pattern of email from an IP over weeks and months, with healthy engagement rates, low complaint rates, and proper authentication, they build a picture of a legitimate sender. New IPs have none of that history.
The moment a new IP or domain sends a large volume of email before establishing any reputation, it looks exactly like what spammers do. Spammers regularly create new sending infrastructure to evade blocks on their existing domains. Inbox providers respond to sudden high-volume sending from unknown sources with aggressive filtering, which is exactly the pattern you want to avoid.
Domain Warming vs IP Warming
IP warming refers specifically to building the reputation of an IP address. If you are using a shared IP through your email service provider, this is usually managed by the provider to some degree. If you are using a dedicated IP, you are responsible for warming it yourself.
Domain warming is about building the reputation of your sending domain. In 2026, domain reputation has become significantly more important than IP reputation for most senders. Even with a well-warmed dedicated IP, a brand new domain needs its own warming period. If you are starting a new domain for cold email outreach, you need to address both.
The IP Warming Timeline: Week by Week
| Week | Daily Send Volume | Recipient Focus | What to Watch For |
| Week 1 | 50 to 100 emails | Highly engaged contacts who regularly open and reply | Authentication passing, zero bounces |
| Week 2 | 200 to 300 emails | Engaged contacts. Open rate should be above 30 percent | Complaint rate, bounce rate |
| Week 3 | 500 to 700 emails | Expand to moderately engaged segment | Monitor Postmaster Tools reputation |
| Week 4 | 1,000 to 1,500 emails | Full engaged list. Begin re-engagement segment | Domain reputation in Postmaster Tools |
| Weeks 5 to 6 | 3,000 to 5,000 emails | Full list minus completely inactive recipients | Spam complaint rate, inbox placement |
| Weeks 7 to 8 | 10,000 or more emails | Full send volume as business requires | All metrics, especially Gmail reputation |
| Adjust Based on Your Metrics
These volume targets are starting points, not fixed rules. If your engagement drops or complaint rates rise during any week, slow down rather than pushing through. Reputation damage that builds during a rushed warm-up can take months to undo. |
Who to Send to During Warm-Up
The quality of recipients you send to during warm-up matters enormously. Sending to your most engaged subscribers, people who regularly open, click, and reply to your emails, generates the positive engagement signals that inbox providers use to evaluate new IPs and domains.
Start with your internal team and colleagues. Then move to your most loyal customers. Only after the first two to three weeks should you start mailing to your broader list. If you are warming a domain specifically for cold outreach, the best approach involves genuine personalised outreach to high-quality prospects who are likely to engage, rather than blasting an unverified cold list.
Common IP Warming Mistakes
- Sending too fast too soon: The single most common mistake. Impatience during warm-up is the main cause of warming failures.
- Using unvalidated lists: Sending to old or unclean lists during warm-up generates high bounce rates at exactly the moment you need clean metrics.
- Skipping authentication setup: Starting to warm a domain before SPF, DKIM, and DMARC are correctly configured means building on a broken foundation.
- Treating warm-up as finished: Reputation building never truly stops. Maintaining consistent practices after warm-up is what sustains the reputation you built.
How FormulaInbox Approaches Warm-Up
When we set up email infrastructure for clients, warm-up is built into the process from the start. Whether you are setting up marketing infrastructure, transactional email, or cold outreach domains, the warm-up approach differs in important ways. Our email infrastructure service includes a tailored warm-up plan as part of every infrastructure engagement.
If you are already in trouble from a failed warm-up, our email deliverability audit diagnoses the specific issues and provides a step-by-step recovery plan. You can start with our free inbox placement test to understand your current situation before deciding on next steps.