> ## Documentation Index
> Fetch the complete documentation index at: https://docs.harpgtm.com/llms.txt
> Use this file to discover all available pages before exploring further.

# Mailbox warm-up and sending limits

> How Harp warms up new mailboxes over 28 days, spaces sends 2 to 6 minutes apart, caps each mailbox per day and times email to the recipient's working hours.

Harp decides when and how fast email goes out, so your agent can decide what to send without putting your domain at risk.

## Warm-up

Every new mailbox warms up over 28 days, starting when it is connected:

| Week | Cold emails per day |
| - | - |
| 1 | 10 |
| 2 | 20 |
| 3 | 30 |
| 4 | 40 |

The cap never goes above the mailbox's own daily limit. Manual and agent sends count toward it too.

Go to **Settings > Integrations > Email delivery** to see each mailbox's warm-up day and today's cap, and to **Start warmup** or **Stop warmup**.

> [!WARNING]
>
> When a mailbox reaches today's cap, sends fail with `DAILY_LIMIT` and resume the next day. Don't raise the limit to get around warm-up.

## Pacing

* Each mailbox waits a random 2 to 6 minutes between sends, so one mailbox sends 10 to 30 emails an hour at most.
* Emails land in the recipient's working hours, in their timezone, when the contact has one.
* Plan large campaigns across several mailboxes, or over more time.

## What every email carries

* A plain-text version alongside the HTML.
* No open or click tracking, unless the workspace turns it on in **Settings > Integrations > Email**.
* A one-click unsubscribe header on cold email. See [Suppression and unsubscribe](https://docs.harpgtm.com/guides/suppression-and-unsubscribe.md).


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