The purpose of dead letter stations in Memphis is pretty much the same – to store poison messages. Poison messages are messages that fail to receive an acknowledgment from the consumer group.

When a consumer consumes a message from the message broker, it sends an acknowledgment, which lets the broker know that the message has been received, and it can send the next one. The broker uses acknowledgments to ensure proper communication. The consumer can also send a negative acknowledgment, i.e., reject a message. So when a consumer gets a message and doesn’t acknowledge or reject it, the broker keeps on retrying to ensure the message is sent to the consumer.

There’s also a predefined number of times (you can configure this value or set it to retry for a certain time period) that a broker will retry the messages before they end up becoming poison.

https://docs.memphis.dev/memphis/memphis/concepts/dead-letter