The last time I looked into this, which was admittedly a long time ago, message-id wasn’t used by all clients for deduping and you had to assume that it wouldn’

The last time I looked into this, which was admittedly a long time ago, message-id wasn’t used by all clients for deduping and you had to assume that it wouldn’t be, so you had to include manual deduping information—-order number etc…