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

# Segments

> The targeting layer: segments define who receives a campaign.

A **segment** is a group of subscribers you can target. Segments are the **targeting layer**: they define **who** receives a campaign, while [topics](/en/guide/topics) define **what**. When you send a campaign, you pick a topic and can narrow it with a segment.

## Segment types

| Type        | Behavior                                                          |
| ----------- | ----------------------------------------------------------------- |
| **Dynamic** | Membership updates automatically based on rules you define.       |
| **Static**  | A group you manage by hand, adding and removing members yourself. |

Segments can be **Active**, **Inactive** or **Archived**.

## Create a segment

In **Segments**, create a new segment via the **Editor** or **Assistant chat** (describe your target audience and the assistant builds the rules; see [Building with the assistant](/en/guide/building-with-ai)):

1. Choose the **type** (dynamic or static).
2. Give it a **name** (3-200 characters) and an optional description.
3. For a dynamic segment, define at least one **rule**.

## Rules (dynamic segments)

Rules are conditions that automatically add matching subscribers.

* Add **conditions** and combine them with **AND / OR** logic.
* Group conditions together for more complex logic.
* Use **Evaluate size** to preview how many subscribers currently match before you save.

The **Rules** tab on a segment's detail view lets you refine these conditions later. You can build rules on subscriber attributes and your [custom fields](/en/guide/custom-fields).

## Members (static segments)

For a static segment, open the **Members** tab to **Add members** or **Remove members**. Search by email or name, filter by topic, and select multiple at once. Save the segment first before managing members.

## Assistant suggestions

Railmail can suggest segments for you under the **Suggestions** tab. Suggestions come from activity, for example **post-campaign** behavior or a **detected pattern**. Each suggestion shows a confidence level, estimated size, a rationale ("why this segment?") and the proposed rules. You can:

* **Approve**: create the segment as suggested.
* **Adjust**: tweak it before creating.
* **Dismiss**: discard it.

<Note>
  These suggestions are controlled by the **Automatic AI segment suggestions** setting in **Settings → Project**, and generating them consumes [AI credits](/en/guide/ai-credits).
</Note>