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

# How the Contacted list prevents duplicates

> Contacted is a system list of everyone you’ve messaged; campaigns use it to avoid messaging the same person twice.

The **Contacted** system list is everyone you’ve ever messaged across linked X accounts, including history synced into Inboxapp. Campaigns use it so the same person isn’t messaged again by accident.

## How it works

When you launch a campaign, Inboxapp typically:

1. Removes prospects on your **excluded lists**
2. Removes people already on **Contacted**

This runs automatically when **Contacted** is excluded. To exclude it in campaign settings: [Prevent messaging leads you’ve already contacted](/help/campaigns/limits-and-safety/how-to-prevent-messaging-leads-you-ve-already-contacted).

## System lists

| List          | Who’s on it                                     | Purpose                    |
| ------------- | ----------------------------------------------- | -------------------------- |
| **Contacted** | Everyone you’ve messaged across linked accounts | Prevent duplicate outreach |
| **Mutual**    | People you follow who follow you back           | Network overlap            |

Contacted and Mutual aren’t ready until DM sync finishes — [How Inboxapp syncs your DMs](/help/getting-started-with-inboxapp/how-inboxapp-syncs-your-dms-and-what-to-expect).

More on both lists: [System lists](/help/leads-management/concepts/understanding-system-lists).

## Related

* [Prevent messaging leads you’ve already contacted](/help/campaigns/limits-and-safety/how-to-prevent-messaging-leads-you-ve-already-contacted)
* [System lists](/help/leads-management/concepts/understanding-system-lists)
* [Reachable vs unreachable leads](/help/leads-management/concepts/understanding-reachable-vs-unreachable-leads)

Still stuck? Contact support from the app.