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IEmail Deliverability Glossary

IP Warm-Up

The process of gradually increasing sending volume from a new IP address to build positive ISP reputation before scaling to full send volume.

IP warm-up is the process of gradually increasing email sending volume from a new or cold IP address to build positive reputation with ISPs before scaling to full sending volume.

Why it's required:

A new IP has zero history. ISPs treat unknown IPs the same way a nightclub bouncer treats someone without ID — they default to skepticism. Gradual warm-up gives ISPs time to observe consistent, low-risk behavior and build a positive trust profile before the IP sends at scale.

IP warm-up principles:

  1. Start with very small volumes (20–100/day for first few days)
  2. Send only to your most engaged, verified subscribers first
  3. Increase volume by no more than 30–50% every few days
  4. Maintain spotless bounce and complaint rates throughout
  5. Monitor Postmaster Tools and SNDS daily during warm-up
  6. Run warm-up traffic simultaneously with dedicated warm-up network sends

IP warm-up timeline:

  • Small volume (< 5k/day): 2–4 weeks
  • Medium volume (5k–50k/day): 4–6 weeks
  • High volume (50k–500k/day): 6–12 weeks

Frequently Asked Questions

How is IP warm-up different from domain warm-up?

IP warm-up builds reputation for a specific IP address. Domain warm-up builds reputation for your sending domain. In practice, these happen simultaneously when you start sending from a new infrastructure — both the IP and domain start with zero history. The key difference is permanence: if your IP gets a bad reputation, you can get a new IP. If your domain reputation gets damaged, it follows your domain indefinitely. This is why domain warm-up is considered more critical — your domain is the identity you're building long-term, while IPs are infrastructure that can be replaced.

What volume should I send on day 1 of IP warm-up?

Start with 20–50 emails on Day 1 for a completely new dedicated IP. This is not a typo — 20 to 50 emails. ISPs need to see a pattern of gradual, consistent growth from unknown senders. Day 1 sends should go to your absolute highest-quality recipients: verified addresses, people who have previously engaged with email from you on other infrastructure, or your warm-up network exclusively. Do not send to cold prospect lists in the first week of IP warm-up. The goal is zero bounces, zero complaints, and maximum positive engagement at this minimal volume.

Do I need to warm up both my IP and domain separately?

They warm up simultaneously — you don't run separate processes for IP and domain. When you send emails during warm-up, ISPs record both which IP sent the message and which domain it came from, building reputation signals for both in parallel. Your warm-up network engagement generates positive signals for both your IP and your domain reputation at the same time. The practical implication: if you change IPs mid-way through warm-up, your domain reputation progress is preserved, but you need to re-warm the new IP from scratch while your domain reputation continues to compound.

Related Terms

C

Cold IP

An IP address with no sending history. ISPs treat unknown IPs with maximum suspicion — sending high volume from a cold IP triggers immediate spam filtering.

D

Dedicated IP

An IP address used exclusively by a single sender. Gives full reputation control but requires complete warm-up from zero before high-volume sending.

E

Email Volume Ramp-Up

The planned, gradual increase in sending volume during warm-up — giving ISPs time to observe positive behavior before large volumes are introduced.

I

IP Reputation

The trust score ISPs assign to a specific sending IP based on bounce rates, complaint rates, spam trap hits, and sending pattern consistency.

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