envelope verifiedcriticalWritten by the Hub
Where failures come back to
The return address used in MAIL FROM — where bounces and delivery notifications arrive, and what receivers check against SPF.
In detail
Distinct from the From: header inside the message, and the distinction matters twice over. Receivers authenticate the envelope address against SPF, so it must belong to a domain whose SPF record authorises the sending address. And bounces go here rather than to the visible sender, which is what makes per-campaign bounce handling possible — a distinct envelope per campaign sorts returns without parsing them. An empty envelope is legitimate and means "do not send me bounces"; it is what automated notifications use so that a bounce cannot bounce.
What happens if you get it wrong
An envelope domain whose SPF does not authorise the sending address.Receivers see an SPF failure, which costs reputation on every message rather than failing loudly once.inference · inference