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# GroupSessionMessenger.DeliveryMode.reliable

An attempt to ensure the delivery of messages to known participants.

```
case reliable
```

## Discussion

Use this approach to send messages that are critical to the experience you
create. The [`GroupSessionMessenger`](/documentation/GroupActivities/GroupSessionMessenger) enqueues a message until it is
successfully transmitted to all known participants.  The system doesn’t guarantee
delivery to participants who join a group session after you send a message, or who
leave the group prior to delivery.

---

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