dsn
Delivery notifications for this message
Which events produce a notification for this message, how much of it is returned, and the identifiers to quote.
In detail
Carries notify, ret, envid and orcpt. The last two are what make notifications machine-readable afterwards: an envelope id quoted back in the report identifies the message without parsing anything. Hub reads outcomes from the result queues instead, so notifications are off on our nodes — but a customer integrating through SMTP submission may rely on them, and then the node must advertise DSN, which it does by default.