You've got a new domain, a new sending IP, or a new ESP account. You have a list of 50,000 people to email. Can you just... send? No. And this week we explain exactly why.
This Week’s Lesson
When a new IP address starts sending email, receiving servers treat it with suspicion. There's no history. No reputation. No data points to suggest the sender is legitimate.
Inbox providers like Gmail and Outlook analyze patterns: Is this IP sending a small amount consistently, or did it suddenly blast 10,000 emails on day one? Sudden, large-volume sends from new IPs are a classic spam signature.
IP warming is the process of gradually increasing send volume over several weeks to build a positive reputation. A typical warm-up schedule might look like: Days 1-5: 20-50 emails/day, Days 6-10: 100-250 emails/day, Weeks 3-4: 500-1,000/day, Month 2: 5,000+/day.
The most important factor during warm-up is engagement. Send your warmest prospects first — people most likely to open, click, and reply. High engagement signals to inbox providers that your emails are wanted.
Domain warming matters too, not just IP warming. A brand-new domain sending email raises flags regardless of which IP it uses. Age, history, and engagement all build domain reputation over time.
Skipping warm-up doesn't just mean some emails go to spam. It can trigger blacklisting that takes weeks to resolve.