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

# Recipients, audience IDs, and batches

> Choose the correct send shape and understand how Signal creates message records

Signal supports direct addresses, one topic audience ID, one segment audience ID, and a batch of independent email requests.
These shapes have different record and response behavior.

## Direct recipients

`to` accepts one address or an array of addresses.
`cc` and `bcc` also accept address arrays and count toward the per-message recipient limit.

When `to` contains multiple direct addresses and both `cc` and `bcc` are empty, Signal fans the request out.
It creates one message per direct recipient and returns a `messages` entry for each recipient.
Each message has its own ID, status, tracking path, and unsubscribe path.

When multiple `to` recipients are combined with `cc` or `bcc`, Signal sends one shared provider message.
That record has an aggregate status and the audience must not be used in this shape.

## Topic audiences

A topic ID begins with `top_`.
It resolves the topic's opt-in subscribers.
The ID must be the only value in `to`, and the request cannot include `cc` or `bcc`.

## Segment audiences

A segment ID begins with `seg_`.
It resolves members of that project segment.
The ID must be the only value in `to`, and the request cannot include `cc` or `bcc`.

Audience sends fan out one message per resolved address.
Signal rejects an empty audience and rejects an audience whose resolved size exceeds 50; it does not silently send only the first 50.
The suppression fence still applies to resolved recipients.

## Batch requests

`POST /v1/emails/batch` accepts up to 100 independent email items.
Each item carries its own sender, recipients, content, schedule, tracking settings, metadata, and idempotency key.

Signal admits the batch atomically: every item is queued or none is queued.
After admission, the items are independent and can reach different delivery outcomes.
Use each response item's index, email ID, and error to correlate results.

## Selection guide

| Requirement                               | Shape                                                |
| ----------------------------------------- | ---------------------------------------------------- |
| One private message per address           | Multiple direct `to` addresses without `cc` or `bcc` |
| One message with shared To/CC/BCC headers | Direct recipients with `cc` or `bcc`                 |
| Every opted-in member of one topic        | One `top_…` value in `to`                            |
| Every member of one static segment        | One `seg_…` value in `to`                            |
| Many unrelated messages in one API call   | Batch endpoint                                       |

<Warning>
  Do not place an audience ID beside an email address or send it as a literal address.
  Signal requires the audience ID to be the only recipient.
</Warning>