It depends on your definition of 'recipient' and 'delivery'. If you assume that the receiver is a specific database instance (or shard) or a specific data store

It depends on your definition of 'recipient' and 'delivery'. If you assume that the receiver is a specific database instance (or shard) or a specific data store (on the receiver side), then it's totally possible to have exactly once delivery in the sense that each message sent would end up being inserted into the database/data store exactly once without duplicates.