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

# Receiving SMS

> How inbound SMS is matched, routed, and assigned.

Inbound SMS arrives on the Twilio webhook for each connected number. The handler:

1. Looks up the **Channel** for the destination number.
2. Searches for an open Conversation that includes the sender's phone number.
3. Creates a new Conversation if none exists, linking it to any records whose phone property matches the sender.
4. Applies the channel's **routing rules** to assign the message to a user (or queue).

## Routing rules

Channel routing rules are evaluated top-down on every inbound message. A rule can match by content keyword, sender area code, time-of-day, or record property. The first matching rule wins. If no rule matches, the channel's default assignment applies.

## Opt-out keywords

`STOP`, `UNSUBSCRIBE`, `END`, `CANCEL`, `QUIT`, and the Spanish equivalents are intercepted by Twilio at the carrier level. These never reach Custral. The number is added to your Twilio account's opt-out list automatically.


## Related topics

- [SMS](/comms/sms/overview.md)
- [Troubleshooting](/comms/sms/troubleshooting.md)
- [Phone](/data/properties/text/phone.md)
- [Suppressions](/comms/suppressions/overview.md)
- [Widgets](/blocks/widgets/overview.md)