# Delivery guarantee ## At most once This guarantee ensures that a message is delivered at most once, but there is a possibility that it may not be delivered at all. ## At least once This guarantee ensures that a message is delivered at least once, but it may be delivered multiple times. ## Exactly once This guarantee ensures that a message is delivered exactly once, and not more or less. ## Links * [Article by Tyler Treat: You Cannot Have Exactly-Once Delivery](https://bravenewgeek.com/you-cannot-have-exactly-once-delivery/) --- # Agent Instructions: Querying This Documentation If you need additional information that is not directly available in this page, you can query the documentation dynamically by asking a question. Perform an HTTP GET request on the current page URL with the `ask` query parameter: ``` GET https://wiki.dmmax.me/distributed-systems/delivery-guarantee.md?ask= ``` The question should be specific, self-contained, and written in natural language. The response will contain a direct answer to the question and relevant excerpts and sources from the documentation. Use this mechanism when the answer is not explicitly present in the current page, you need clarification or additional context, or you want to retrieve related documentation sections.