# Email warm-up: raising send volume slowly

Email warm-up means starting a new domain or provider at low volume to engaged people and ramping up. How it works, and the controls Mimeo gives you.

**Definition:** Email warm-up is starting a new sending domain, IP or provider at low volume, to your most engaged people, then raising volume step by step so inbox providers learn to trust your mail.

## How it works

Mailbox providers judge mail partly by its history. A domain with no history, or one whose volume suddenly jumps, gets treated with caution. Warm-up builds that history on purpose: small sends to the people likeliest to open, then larger ones, checking bounces and complaints between steps.

Google's sender guidelines say to start with a low volume to engaged users, increase it slowly, and avoid bursts. Suddenly doubling your usual volume can bring rate limiting or a reputation drop. Resend's warm-up guide applies the same idea whenever you use a new domain, IP or provider, or your volume will grow. It asks you to keep bounces below 4% and spam complaints below 0.08% while you ramp up, and to slow down if either rises.

A typical plan for an existing list moving to a new provider:

1. First send: a small cohort of your most engaged subscribers.
2. Next send: that cohort plus another engaged batch, if the first results were clean.
3. Then the rest, once bounces and complaints stay low.

## Why it matters

- **The first big send is the riskiest.** Skip warm-up and it can be throttled, deferred or filtered to spam.
- **Damage outlasts the send.** A reputation drop affects the sends that follow, not just the one that caused it.
- **Switching platforms counts.** A new sending provider, and often a new domain, starts with little history.

## How Mimeo handles it

Mimeo doesn't deliver your mail: your own Postmark or Resend account does. Warm-up is a plan you run, and Mimeo gives you the controls for it. Its migration docs set out a [three-newsletter transition](https://mimeohq.com/docs/usage/migrating#warm-up-before-you-blast): a small, engaged first cohort, expanded only when delivery results hold.

You pick each cohort with a [segment](https://mimeohq.com/docs/usage/segments), on a migration tag such as `migration-wave-1` or on engagement data you brought from the old tool. Every [broadcast drains at a set pace](https://mimeohq.com/docs/usage/broadcasts#the-sending-pace), most engaged people first, so the warmest addresses lead and a send going wrong can be canceled with most of it still queued. After each send, reports show bounces and complaints. See [Mimeo terms](https://mimeohq.com/docs/glossary#sending--deliverability) for warm-up in Mimeo's own words.

## Sources

1. [Email sender guidelines](https://support.google.com/a/answer/81126), checked 2026-11-09
2. [Domain and/or IP warm-up guide](https://resend.com/docs/knowledge-base/warming-up), checked 2026-11-09
3. [Migrating from another email platform](https://mimeohq.com/docs/usage/migrating), checked 2026-11-09
4. [Broadcasts](https://mimeohq.com/docs/usage/broadcasts), checked 2026-11-09
5. [Segments](https://mimeohq.com/docs/usage/segments), checked 2026-11-09

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This is the Markdown copy of https://mimeohq.com/glossary/email-warm-up.