IP Warming
Also known as: IP Warm-Up, IP Reputation Warming
Gradually increasing email volume from a new dedicated IP address to establish positive sender reputation with inbox providers.
Definition
IP warming is the practice of slowly ramping up sending volume from a new dedicated IP address so mailbox providers can observe healthy sending patterns and build a positive reputation for that IP. Like domain warming, it follows a schedule that roughly doubles volume every 3-4 days over 4-8 weeks.
IP warming used to be critical for every sender because most mail traveled from sender-controlled IPs. Today, most senders use shared IPs from reputable Email Service Providers (Resend, Postmark, SendGrid, AWS SES) — the provider has already warmed those IPs and shares the reputation pool across clients.
Dedicated IPs are still common for high-volume senders (1M+ emails/month), regulated industries (finance, healthcare) that need IP isolation, and senders who want full reputation control. For everyone else, shared infrastructure is the right default.
Why It Matters
An un-warmed dedicated IP is treated as a stranger by mailbox providers. The first 50,000 emails from a cold IP will see open rates of 5-10% (vs the 30%+ a warmed IP would see) and the IP may get added to gray-list or block-list databases within 24 hours.
The biggest mistake is migrating to a dedicated IP without a warming plan because your previous shared-IP setup 'worked fine.' A new IP starts with zero reputation regardless of your domain's history — you have to rebuild trust IP-by-IP.
Examples in Practice
A SaaS company sending 500K emails/month migrates from a shared-IP provider to a dedicated IP. Day 1: 1,000 emails to most-engaged users. Day 4: 2,500. Day 7: 5,000. By week 4 they're at 20,000/day; by week 8 they're at full volume with stable deliverability.
A team launches a dedicated IP and immediately sends a 100,000-recipient newsletter. Day 1 open rate: 6%. The IP is gray-listed by Gmail and several corporate filters within 24 hours. Recovery takes 4-6 weeks of conservative sending plus appeals to spam-trap operators.
An e-commerce business stays on shared IPs because their volume (under 200K/mo) doesn't justify the operational overhead of a dedicated IP. They focus engineering attention on domain reputation and content quality instead — and see better deliverability than competitors running un-warmed dedicated IPs.