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

# Contacts Overview

> An overview of contacts in Conversion.

Contacts are the core of Conversion. A contact represents a single individual in your database: someone who has filled out a form, been imported, synced from Salesforce, or created through your data warehouse or API.

## Contact Identity

Every contact in Conversion has an email address. Conversion uses **strong identifiers** to track contacts across different data sources:

| Source         | Strong Identifier | Why It's Authoritative                                 |
| :------------- | :---------------- | :----------------------------------------------------- |
| Salesforce     | Salesforce ID     | Unique per Lead/Contact; survives email changes        |
| Forms          | Email address     | Identifies contacts via the "email address" form field |
| Data Warehouse | `userId`          | Your system's stable internal user ID                  |
| API            | `userId`          | Same stable identifier used by your systems            |

<Tip>
  Matching by strong identifiers helps handle cases where emails are duplicated in your systems, and prevents unintended data overwrites.
</Tip>

When data arrives from any source, Conversion follows these rules in order:

1. Check for a **matching strong identifier.** If one is found, the existing contact is updated.
2. Look for the most recently updated contact with the **same email address** that doesn't already have a strong identifier, and link the new identifier.
3. If no matched contact was found, create a new contact.

***

## What's Stored on a Contact

Each contact in Conversion includes:

* **Email address** (required)
* **Strong identifiers** linking the contact to external systems (Salesforce ID, cookie, userId)
* [Default fields](/product-docs/records/contacts/default-fields) like first name, last name, phone, job title, city, and more
* [Custom fields](/product-docs/sync/salesforce/custom-fields) that sync from your Salesforce Lead and Contact fields
* [System fields](https://docs.conversion.ai/data-management/fields/reference#system-managed-contact-fields) like traffic source, UTM parameters, and system source (automatically tracked)
* **A link to their company** (every contact belongs to one company)

***

## Salesforce Leads and Contacts Both Sync to Conversion Contacts

Whether someone is a Lead or a Contact in Salesforce, they become a contact in Conversion. Conversion tracks which Salesforce record they're linked to via the Salesforce ID, so:

* Updates in Salesforce flow to the right Conversion contact
* Changes you make in Conversion can sync back to the correct Salesforce record
* If a Lead converts to a Contact in Salesforce, Conversion automatically re-links to the new Contact record

***

## Duplicate Contacts

Because Conversion allows duplicate email addresses, it's possible for more than one contact to share the same email. This typically happens when:

* A Salesforce record syncs and the matching email is already linked to a different Salesforce ID
* A data warehouse record syncs with a userId that conflicts with an existing contact's userId
* A contact is created manually in the dashboard with an email that already existsHow contacts enter Conversion

### Email Sending to Duplicate Email Addresses

Because duplicate email addresses can exist across contacts, Conversion handles email sending carefully to avoid over-emailing.

#### Blasts (One-Time Emails)

When you send a blast, Conversion deduplicates by email address. If multiple contacts with the same email are in the audience, the email is sent only once -- to the most recently updated contact. Engagement activity (opens, clicks, etc.) is attributed to that contact.

#### Workflow Emails

In workflows, each contact progresses independently. Conversion uses **communication limits** (configured at the organization level) to prevent the same email address from receiving too many emails within a given time period, regardless of how many contacts share that address.

***

## What's next

<CardGroup cols={2}>
  <Card title="Viewing Contacts" icon="table" href="/product-docs/records/contacts/viewing-contacts">
    Filter, search, and organize your contact list with views and columns.
  </Card>

  <Card title="Creating Contacts" icon="user-plus" href="/product-docs/records/contacts/creating-contacts">
    Add contacts manually or import them from a CSV.
  </Card>

  <Card title="Contact Record" icon="address-card" href="/product-docs/records/contacts/contact-record">
    View and edit a contact's details, company info, and system metadata.
  </Card>

  <Card title="Activity" icon="clock-rotate-left" href="/product-docs/records/contacts/activity">
    Explore the full activity log and engagement history on a contact.
  </Card>
</CardGroup>