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title: Configure the Quality of Service for MQTT Connector
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# Configure the Quality of Service for MQTT Connector

> For the full documentation index, see: https://docs.mulesoft.com/llms.txt

The MQTT protocol enables you to specify levels of delivery assurance for inbound or outbound
messages. These levels are referred to as _quality of service_ (QoS).

The available QoS levels to configure for MQTT Connector are:

- **AT\_MOST\_ONCE**

  Messages are delivered at most one time ("fire and forget") and delivery is not guaranteed.

- **AT\_LEAST\_ONCE**

  Messages are delivered correctly at least one time. The message could be delivered more than once.

- **EXACTLY\_ONCE**

  Messages are sent once and delivery is ensured.

The quality of service is sometimes different between message publishing and message subscribing,
even if the published message and the subscription have a common topic. For example, a message
published with QoS 1 or 2 might not be successfully delivered to the **On New Message** source, if
that listener source is subscribed with QoS **AT\_MOST\_ONCE** (QoS=0).

## See Also

- [MQTT3 Connector Examples](https://docs.mulesoft.com/mqtt3-connector/1.0/mqtt3-connector-examples)

- [Salesforce Help](https://help.salesforce.com)