---
title: Protocol Selection | API Docs
description: How the API picks between iMessage, RCS, and SMS for message delivery.
---

The Linq API sends messages over iMessage, RCS, and SMS. See the [Create Chat](/channel/imessage/api/resources/chats/methods/create/index.md) API reference for the full specification.

## Automatic selection

Every send uses the richest protocol the recipient supports, in the order **iMessage → RCS → SMS**. The `service` field on the message and its webhooks reports the protocol used for delivery.

Note

`preferred_service` is deprecated. Omit it from new sends.

## Protocol capabilities

Not all features are available on every protocol:

| Feature                                                                             | iMessage | RCS     | SMS |
| ----------------------------------------------------------------------------------- | -------- | ------- | --- |
| Text messages                                                                       | Yes      | Yes     | Yes |
| Images & video                                                                      | Yes      | Yes     | MMS |
| Read receipts                                                                       | Yes      | Yes     | No  |
| Delivery receipts                                                                   | Yes      | Yes     | No  |
| [Typing indicators](/channel/imessage/guides/chats/typing-indicators/index.md)      | Yes      | No      | No  |
| [Reactions](/channel/imessage/guides/messaging/reactions/index.md) / tapbacks       | Yes      | Yes     | No  |
| [Message effects](/channel/imessage/guides/messaging/message-effects/index.md)      | Yes      | No      | No  |
| [Group chats](/channel/imessage/guides/chats/group-chats/index.md)                  | Yes      | Yes     | MMS |
| Message threading                                                                   | Yes      | No      | No  |
| Rich link previews                                                                  | Yes      | Yes     | No  |
| [Voice memos](/channel/imessage/guides/messaging/voice-memos/index.md)              | Yes      | Yes     | No  |
| [File attachments](/channel/imessage/guides/messaging/attachments/index.md) (100MB) | Yes      | Limited | No  |
| Text decorations                                                                    | Yes      | No      | No  |
| [Location sharing](/channel/imessage/guides/location-sharing/index.md)              | Yes      | No      | No  |

## Checking support before you send

To decide whether to use an iMessage-only feature such as message effects or text decorations, check the recipient first with the capability endpoints. See [Capability Checks](/channel/imessage/guides/chats/capability-checks/index.md).