# Reference

Message parts, status and error codes, and how opt-outs are handled.

Detailed reference for how messages are counted, the status and error codes you may see, and how opt-out requests are handled.

## Pages in this section

- [SMS message parts](https://iflow.net/docs/reference/sms-message-parts/): Why long messages and emoji cost more: SMS parts, the 160 and 70 character limits, and the basic and Unicode character sets.
- [Status and error codes](https://iflow.net/docs/reference/sms-status-codes/): Every status and error code an Iflow message or job can show, and what each one means.
- [Opt-outs and the stop list](https://iflow.net/docs/reference/opt-outs/): How Iflow handles opt-out requests automatically, using the opt-out instruction, the STOP keyword and your stop list.

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Source: https://iflow.net/docs/reference/