What is “cold” vs “warm” IP reputation?
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When you start sending from a brand new IP address, mailbox providers have no idea who you are. No sending history, no track record, nothing. That's a cold IP: an IP with no established reputation. Gmail and Outlook treat it with suspicion by default, applying tight rate limits and extra filtering until it proves itself.
A warm IP is the opposite: consistent sending history, low complaint rates, decent engagement, clean bounces. Mailbox providers have seen this IP behave well over time, so they give it more throughput and better inbox placement.
IP warming is the process of building that reputation from scratch. You can't start a new IP at full volume. You have to earn the right to send more. A typical schedule looks something like this:
- Week 1: 1,000 to 5,000 emails per day
- Week 2: 5,000 to 15,000 emails per day
- Week 3: 15,000 to 50,000 emails per day
- Week 4 onwards: scale up based on your metrics
During warming, send to your most engaged subscribers first. Opens, clicks, and low complaints are the signals that tell mailbox providers this IP is sending mail people want. If you blast your full list cold, you'll get complaints from disengaged subscribers before you've built any goodwill, and the IP stays cold or gets flagged.
You can check whether a new IP is already being flagged or rate-limited with our free blocklist checker. And if warming is stalling or your metrics are going sideways, the SOS hotline is free.
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