IP warming: how to build reputation on a new address

IP warming is the practice of sending small email volumes from a new or dormant IP address, then gradually increasing that volume over 2–6 weeks until you reach your normal sending rate. Mailbox providers track how recipients respond to mail from each IP. An unknown IP sending 100,000 messages on day one looks like a spam blast, because that is exactly what spam blasts look like.

Typical warming schedule

The standard approach doubles daily volume every two to three days. Example for a target of 100,000 per day: Day 1–2: 500. Day 3–4: 1,000. Day 5–6: 2,000. Day 7–8: 5,000. Day 9–10: 10,000. Day 11–12: 25,000. Day 13–14: 50,000. Day 15+: 100,000. Real timelines vary with list quality and how your subscriber base is distributed across providers. If 70% of your list is on Gmail, calibrate the pace against Gmail's own limits specifically.

Who to send to first

During warming, audience quality matters more than anything else. First messages should go to your most engaged subscribers: people who opened or clicked something in the last 30 days. Their positive responses give providers a reason to trust the new address. Sending to cold or unverified contacts at this stage can push bounce rate above 2% before you have built any goodwill. That is a hard position to recover from.

What to watch

Bounce rate should stay below 2%. If it climbs higher, stop and clean the list before continuing. Complaint rate should stay below 0.1%. SMTP response codes: a 421 (temporary reject) or 452 (too many connections) means you have exceeded the provider's pace limit. Hold volume for 2–3 days before increasing again. Open rate should run above your usual average, since you are sending to your best segment.

Common mistakes

Ramping every day instead of every two to three. Using an unverified list. Taking days off — gaps slow reputation formation because providers see inconsistent volume as suspicious. Treating the schedule as fixed: if bounce rate spikes to 5% on day three, pausing to investigate is the right call, not moving to the next step anyway.