Having built something similar with RabbitMQ in a high-volume industry, there are a lot of benefits people in this thread seem to be glossing over and are instead debating semantics. Yes, this is not "exactly once" -- there really is no such thing in a distributed system. The best you can hope for is that your edge consumers are idempotent.
There is a lot of value derived from de-duping near ingress of a heavy stream such as this. You're saving downstream consumers time (money) and potential headaches. You may be in an industry where duplicates can be handled by a legacy system, but it takes 5-10 minutes of manual checks and corrections by support staff. That was my exact use case and I can't count the number of times we were thankful our de-duping handled "most" cases.
There is a lot of value derived from de-duping near ingress of a heavy stream such as this. You're saving downstream consumers time (money) and potential headaches. You may be in an industry where duplicates can be handled by a legacy system, but it takes 5-10 minutes of manual checks and corrections by support staff. That was my exact use case and I can't count the number of times we were thankful our de-duping handled "most" cases.