"Return-Path". Used to convey the information from the MAIL FROM envelope attribute in final delivery, when the message leaves the SMTP environment in which "MAIL FROM" is used. RFC 821, 1123.

Public Const ReturnPath As String

Dim value As String
 
value = HeaderKey.ReturnPath

public const string ReturnPath

public: const string* ReturnPath

public:
const String^ ReturnPath