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The chart below summarizes how Quality of Service (QOS), Clean Session flag and Retain Message flag affects what messages are receivedpersisted.
| Retain Message flag | Clean Session flag | Subscribe QOS | Publish QOS | Published Message Persisted |
|---|
| False | True | 0 | 0 | No |
| False | True | 0 | 1 or 2 | No |
| False | True | 1 or 2 | 0 | No |
| False | True | 1 or 2 | 1 or 2 | No |
| False | False | 0 | 0 | No |
| False | False | 0 | 1 or 2 | No |
| False | False | 1 or 2 | 0 | No |
| False | False | 1 or 2 | 1 or 2 | Yes - all messages |
| True | True | 0 | 0 | Yes - last message only for each unique MQTT topic |
| True | True | 0 | 1 or 2 | Yes - last message only for each unique MQTT topic |
| True | True | 1 or 2 | 0 | Yes - last message only for each unique MQTT topic |
| True | True | 1 or 2 | 1 or 2 | Yes - last message only for each unique MQTT topic |
| True | False | 0 | 0 | Yes - last message only for each unique MQTT topic |
| True | False | 0 | 1 or 2 | Yes - last message only for each unique MQTT topic |
| True | False | 1 or 2 | 0 | Yes - last message only for each unique MQTT topic |
| True | False | 1 or 2 | 1 or 2 | Yes - all messages |
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