Property Value

Type: String
A string value with the diagnostic code from "Diagnostic-Code" DSN field, or a null reference (Nothing in Visual Basic) if no such field contained in the DSN.

When Action is Failed or Delayed for the given recipient, this field contains the actual diagnostic code issued by the mail transport. Since such codes vary from one mail transport to another, the diagnostic-type subfield is needed to specify which type of diagnostic code is represented.

In this example, DSN field is:
Diagnostic-Code: smtp; Permanent Failure: Other undefined Status
The return value is marked bold.