IP warmup

IP warmup is the practice of gradually ramping send volume from a new dedicated sending IP so that mailbox providers can build a positive reputation for the IP before it carries real campaign traffic.

What it is

IP warmup is the older, IP-centric cousin of domain warmup. When you provision a new dedicated IP from an ESP — SendGrid, Postmark, SES, or your own MTA — that IP arrives at every mailbox provider with no history. Spam filters treat it with suspicion: a previously dormant IP that suddenly starts blasting 50,000 messages a day is the exact fingerprint of compromised infrastructure. So the IP gets throttled, deferred, or sent straight to spam.

Warmup defuses that by starting small — a few hundred messages on day one — and doubling each day, watching engagement metrics carefully and scaling back if complaints rise. By the end of the ramp the IP has a documented track record and the mailbox providers' internal scores treat it like a normal sender.

How it differs from domain warmup

Domain warmup builds reputation for the d= domain in your DKIM signature — the identity that travels with your mail regardless of which IP delivered it. IP warmup builds reputation for the specific IPv4 (or IPv6) address. They're complementary, not interchangeable.

Modern mailbox providers weight domain reputation more heavily than IP reputation, because spammers can churn through IPs cheaply but burn domains more slowly. For cold-email specifically — where most senders run on shared IPs anyway — domain warmup is the relevant exercise. IP warmup matters only if you control your own dedicated IP.

When you actually need it

You need a dedicated IP — and therefore IP warmup — when your monthly volume exceeds roughly 100,000 messages from a single domain, or when you're a transactional sender who wants total control over IP reputation. Below that volume, the math doesn't work: a dedicated IP won't accumulate enough engagement signal to score well, and you're better off on a curated shared pool.

Most cold-email senders running through Instantly, Smartlead, or similar tools share IPs by default. They don't need IP warmup. What they need is template-based warmup of the sender identity and the message content.

A typical schedule

A standard 30-day IP warmup looks something like this: day 1, send 50 messages, half to Gmail and half to Outlook, all to your most engaged subscribers. Day 2, double to 100. Day 3, 200. Continue doubling daily through day 7. From day 8 increase by roughly 30 percent per day. By day 14 you should be at roughly 10,000 per day, and by day 30 you can sustain 200,000+ daily on a single IP if engagement holds. Watch your Postmaster Tools data daily — any spike in spam rate or drop in inbox placement is your signal to pause the ramp.

Why it matters

Skip IP warmup on a new dedicated IP and the first big send will fail loudly. Throttling at Gmail, hard rejects at Outlook, and a 30 percent spam-folder rate are typical. Recovering takes weeks of clean engagement. The warmup process is cheap; the alternative is not.

Related

• Email warmup — the umbrella term
• Template-based warmup — the content layer
• Sender reputation — what warmup builds
• Email warmup guide for 2026
• How NeverSpam approaches sender warmup