用VB实现一个简单的ESMTP客户端

Text2.Text))
End Sub

Private Sub Command2_Click()
    state = 0
    smtpClient.Close
    smtpClient.Connect
End Sub

Private Sub Form_Load()
    mailcount = 2
    FLAG_LINE_END = Chr(13) + Chr(10)
    FLAG_MAIL_END = FLAG_LINE_END + "." + FLAG_LINE_END
End Sub

Private Sub Form_Terminate()
    smtpClient.Close
End Sub

Private Sub smtpClient_Close()
    ''MsgBox "closed!"
    state = 0
End Sub

Private Sub smtpClient_DataArrival(ByVal bytesTotal As Long)
    Dim s As String
    smtpClient.GetData s
    Text1.Text = Text1.Text + s + FLAG_LINE_END
    Dim msgHead As String
    msgHead = Left(s, 3)
    Dim msgBody As String
    msgBody = Mid(s, 5)
    
    Dim msgType As Integer
    msgType = CInt(msgHead)
    Dim msgsend As String
    
    Select Case state
    Case 0  ''start state
        Select Case msgType
        Case 220
            msgsend = "EHLO yourname" + FLAG_LINE_END
            smtpClient.SendData msgsend
            Text1.Text = Text1.Text + msgsend + FLAG_LINE_END
            state = 1
        Case 421    ''Service not available
        End Select
    Case 1  ''EHLO
        Select Case msgType
        Case 250
            msgsend = "AUTH LOGIN" + FLAG_LINE_END
            smtpClient.SendData msgsend
            Text1.Text = Text1.Text + msgsend + FLAG_LINE_END
            state = 2
        Case 500, 501, 504, 421 ''error happened
        End Select
    Case 2  ''AUTH LOGIN
        Select Case msgType
        Case 334
            If msgBody = "VXNlcm5hbWU6" + FLAG_LINE_END Then
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