public string Status { get; }

Public ReadOnly Property Status As String
	Get

Property Value

The per-recipient Status field contains a transport-independent status code which indicates the delivery status of the message to that recipient. This field MUST be present for each delivery attempt which is described by a DSN.

Status codes thus consist of three numerical fields separated by dot ("."). The first sub-field indicates whether the delivery attempt was successful (2 = success, 4 = persistent temporary failure, 5 = permanent failure). The second sub-field indicates the probable source of any delivery anomalies, and the third sub-field denotes a precise error condition, if known.

In this example, DSN field is:
Status: 5.1.1
The return value is marked bold.

Reference