IP Warm-up: Why It Matters and How to Do It Right
IP warm-up is the process of gradually building sender reputation on a new IP address. Get it wrong and you'll send yourself to spam from day one. This guide explains how it works and how to automate it.
When you set up a new dedicated sending IP, it arrives with no history — no reputation, no relationships with inbox providers, no track record. To the spam filters at Gmail, Outlook, and Yahoo, a brand new IP address looks exactly like a spammer's IP looks: unknown, untrustworthy, and suspicious.
IP warm-up is the process of establishing a positive reputation on that new IP by gradually ramping up sending volume over several weeks, giving inbox providers time to observe your sending patterns and confirm that you're a legitimate sender.
How ISPs evaluate new IPs
Inbox providers watch several signals when they see mail from an unfamiliar IP: the volume of mail being sent, the ratio of delivered mail to bounces, the spam complaint rate, whether recipients are engaging with the mail (opens and clicks), and whether the IP is on any blocklists.
In the early days of warming up an IP, providers typically accept a small volume and throttle the rest. As your reputation builds — as they see that bounces are low, complaints are minimal, and recipients are opening your emails — they gradually accept higher volumes from your IP.
A typical warm-up schedule
A conservative warm-up schedule for a new dedicated IP typically looks like this: 500 per day in the first 3 days, 2,000 per day in days 4–7, 5,000 per day in week 2, 15,000 per day in week 3, 40,000 per day in week 4, and full volume in week 5 and beyond. The exact pace depends on your engagement metrics along the way.
"The most important rule of IP warm-up: send only to your most engaged subscribers first. If your first sends have low open rates and high complaints, you'll establish a bad reputation that's hard to recover from."
What to send during warm-up
During warm-up, send only to your highest-quality subscribers — people who have opened your email in the last 30–60 days. High engagement signals during warm-up establish a positive reputation faster. Avoid sending to your entire list, especially stale segments that haven't engaged in months.
Automated warm-up with Sendbound
Sendbound automates the entire warm-up process. When you get a new dedicated IP, Sendbound's warm-up scheduler calculates a day-by-day ramp based on your list size and engagement data. It monitors bounce rates, complaint rates, and ISP throttle signals in real time and adjusts the schedule automatically — sending less on days when signals are negative, accelerating on days when everything looks healthy. You don't need a spreadsheet or a deliverability consultant. You just turn it on.
Shared vs. dedicated IPs
If you're sending fewer than 50,000 emails per month, you're likely on a shared IP pool — your emails share an IP with other senders on the same platform. This means you benefit from the established reputation of the pool, but you're also exposed to other senders' bad behavior. Once you're above 50,000 monthly sends, a dedicated IP gives you full control over your reputation and is worth the warm-up investment.