IsFailed returns true if Action field is "failed", meaning message could not be delivered to the recipient.

ParseReport parses p as a "container" for delivery status report (per rfc6522) if p is "multipart/report".

DeliveryStatus provides a machine-readable description of the condition(s) that caused the report to be generated.

Explanation contains a human-readable description of the condition(s) that caused the report to be generated.

Report represents delivery status report as per https://datatracker.ietf.org/doc/html/rfc6522.