Suppression list verifiedimportantWritten by the Hub
Addresses and domains that are failed on sight, each with the code and text the failure carries.
In detail
The list is checked at delivery time, so adding an entry also stops messages already queued for that recipient. Each row carries the SMTP code, the extended status and the description that the failure will report — which means the reason travels into the result stream and into our own statistics. The screen writes through /suppression; the REST endpoint requires a type field this form fills in itself.