用VB实现一个简单的ESMTP客户端

sp;               msgsend = base64encode(utf16to8("username")) + FLAG_LINE_END
                smtpClient.SendData msgsend
                Text1.Text = Text1.Text + msgsend + FLAG_LINE_END
            ElseIf msgBody = "UGFzc3dvcmQ6" + FLAG_LINE_END Then
                msgsend = base64encode(utf16to8("password")) + FLAG_LINE_END
                smtpClient.SendData msgsend
                Text1.Text = Text1.Text + msgsend + FLAG_LINE_END
            End If
        Case 235    ''correct
            SetFrom "you@domain.com"
            state = 3
        Case 535    ''incorrect
            Quit
            state = 7
        Case Else
        End Select
    Case 3  ''FROM
        Select Case msgType
        Case 250
            SetRcpt "rpct@domain.com"
            state = 4
        Case 221
            Quit
            state = 7
        Case 573
            Quit
            state = 7
        Case 552, 451, 452  ''failed
        Case 500, 501, 421  ''error
        End Select
    Case 4  ''RCPT
        Select Case msgType
        Case 250, 251  ''user is ok
           &nbs