(custom properties) critical
Our own fields, returned
Properties the job carried that MailerQ does not recognise come back untouched.
In detail
The mechanism that makes correlation free. A campaign id, a plan number or an audience reference put into the job arrives in the result Hub already collects — no second call, no matching by timestamp, no dependence on the engine's own identifier. This is the field Hub's MailerQ telemetry should be built around, precisely because message-id is not safe across a fleet while server-id is unset.