An option might be to fix your message IDs, e.g. something like 20230413-userid@yourapp. Let the recipient's email server de-duplicate if you are not sure you c

An option might be to fix your message IDs, e.g. something like 20230413-userid@yourapp. Let the recipient's email server de-duplicate if you are not sure you can do better than at-least-once delivery on your side.