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Receiving response from POP3 mail server

, 8 Jan 2013
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Receiving response correctly from pop mail server is the first step on receiving emails to your own email client.

Introduction

This article discusses how to successfully receive a response from a pop3 mail server (i.e. Gmail) using your programming skills, not just a third party class, using .NET Framework 4 and VB2010 (TcpClient) class.

This is more like a full E-mail client project but still in the beginning, so this will be updated many times . 

Background

Since Microsoft did not release a POP3 class that directly enables programmers to use in order to interact with mail servers (i.e., Gmail) to download emails of their own or provide applications for clients that helps in receiving email from email servers, i thought it would be OK to start my own project using the VB2010 along with .Net framework technology.

Also i want to say that most of the vb.net application i downloaded and tested did not really work for me for many reasons such as they are old posts or using the wrong settings or written in different languages like C#, C++ or java, so i really wanted to create a VB.Net example using only VB.Net tools. 

Using the code

I'm using : WinXPSp3, VB2010 Pro. and .NET Framework 4

No special functions or anything just a very simple way to receive response from Gmail pop server.

I have only one form in my VB2010 project called [Form1] and here is a picture for it:

Front form 

So all you need to do is create a new project and save it to your hard desk.

The code goes like this : 

' start from here.
Imports System.IO
Imports System.Net.Sockets
Imports System.Text
Imports System.Net.Security
Imports System.Net

   Class Form1
    Dim PopHost As String
    Dim UserName As String
    Dim Password As String
    Dim PortNm As Integer

    Dim POP3 As New TcpClient
    Dim Read_Stream As StreamReader
    Dim NetworkS_tream As NetworkStream
    Dim m_sslStream As SslStream
    Dim server_Command, Sent_Val As String
    Dim m_buffer() As Byte
 
 Private Sub CmdDownload_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles CmdDownload.Click

        PopHost = TxtHost.Text
        UserName = TxtUsrNm.Text
        Password = TxtPass.Text
        PortNm = TxtPort.Text
        Cursor = Cursors.WaitCursor
        POP3.Connect(PopHost, Integer.Parse(PortNm))
        Login

        Cursor = Cursors.Default
    End Sub

    Sub Login()
        NetworkS_tream = POP3.GetStream()
        m_sslStream = New SslStream(NetworkS_tream)
        m_sslStream.AuthenticateAsClient(PopHost)
        Read_Stream = New StreamReader(m_sslStream)
        ListBox1.Items.Add(Read_Stream.ReadLine())

        server_Command = "USER " + UserName + vbCrLf
        m_buffer = System.Text.Encoding.ASCII.GetBytes(server_Command.ToCharArray())
        m_sslStream.Write(m_buffer, 0, m_buffer.Length)
        ListBox1.Items.Add(Read_Stream.ReadLine())

        server_Command = "PASS " + Password + vbCrLf
        m_buffer = System.Text.Encoding.ASCII.GetBytes(server_Command.ToCharArray())
        m_sslStream.Write(m_buffer, 0, m_buffer.Length)
        ListBox1.Items.Add(Read_Stream.ReadLine())

        'Send STAT command to get information ie: number of mail and size
        server_Command = "STAT " + vbCrLf
        m_buffer = System.Text.Encoding.ASCII.GetBytes(server_Command.ToCharArray())
        m_sslStream.Write(m_buffer, 0, m_buffer.Length)
        ListBox1.Items.Add(Read_Stream.ReadLine())

    End Sub

End Class  
'Ends here.  

Update (1) 17, Aug, 2012 : Retrieve the Number of E-mails from Inbox 

Code for update (1) : 

        'Get Messages count
        Dim server_Stat(2) As String
        server_Stat = StatResp.Split(" ")
        MsgCount.Text = server_Stat(1) 

Link for update NO. 1 - Here 


This update discusses : 

  • The difference between Get Emails from Gmail.com and Hotmail.com
  • Setting up your Gmail.com account to receive the new unread e-mails or the total number of E-mails generally. 
  • Hotmail.com server won't show the difference between the unread E-mails or the total number of E-mails. 
  • Receiving the number of E-mails in a TextBox control [MsgCount]. 
Photo for update (1) :  

 

Update (2) 18, Aug, 2012 : Download E-mails from POP3 Server into TextBox 

Code for update (2) : This will be a replace of the main code above . 

        'Starts
Imports System.IO
Imports System.Net.Sockets
Imports System.Text
Imports System.Net.Security
Imports System.Net
Class Form1
    Dim PopHost As String
    Dim UserName As String
    Dim Password As String
    Dim PortNm As Integer

    Dim POP3 As New TcpClient
    Dim Read_Stream As StreamReader
    Dim NetworkS_tream As NetworkStream
    Dim m_sslStream As SslStream
    Dim server_Command As String
    Dim ret_Val As Integer
    Dim Response As String
    Dim Parts() As String
    Dim m_buffer() As Byte
    Dim StatResp As String
    Dim server_Stat(2) As String
    Private Sub CmdDownload_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles CmdDownload.Click
        'If statement is to control the login and logout method : Exception (Already Connected TcpClient)
        If POP3.Connected = True Then
            CloseServer()
            POP3 = New TcpClient(PopHost, Integer.Parse(TxtPort.Text))
            ret_Val = 0
            Exit Sub
        Else

            PopHost = TxtHost.Text
            UserName = TxtUsrNm.Text
            Password = TxtPass.Text
            PortNm = TxtPort.Text


            Cursor = Cursors.WaitCursor
            POP3 = New TcpClient(PopHost, Integer.Parse(TxtPort.Text))

            NetworkS_tream = POP3.GetStream 'Read the stream
            m_sslStream = New SslStream(NetworkS_tream) 'Read SSL Stream
            m_sslStream.AuthenticateAsClient(PopHost) 'Auth.
            Read_Stream = New StreamReader(m_sslStream) 'Read the stream
            StatResp = Read_Stream.ReadLine()

            ListBox1.Items.Clear()
            StatResp = Login(m_sslStream, "USER " & UserName) & vbCrLf
            ListBox1.Items.Add(StatResp)
            StatResp = Login(m_sslStream, "PASS " & Password) & vbCrLf
            ListBox1.Items.Add(StatResp)
            StatResp = Login(m_sslStream, "STAT ") & vbCrLf
            ListBox1.Items.Add(StatResp)

            'Get Messages count
            server_Stat = StatResp.Split(" ")
            MsgCount.Text = server_Stat(1)
            ret_Val = 1
        End If

        Cursor = Cursors.Default
        CmdClose.Enabled = True
        CmdDownload.Enabled = False
    End Sub
    Sub CloseServer()
        StatResp = Login(m_sslStream, "QUIT ") & vbCrLf
        ListBox1.Items.Add(StatResp)
        ListBox2.Items.Clear()
        TextBox1.Text = String.Empty
        POP3.Close()
        ret_Val = 0
    End Sub
    Function Login(ByVal SslStrem As SslStream, ByVal Server_Command As String) As String
        Dim Read_Stream2 = New StreamReader(SslStrem)
        Server_Command = Server_Command + vbCrLf
        m_buffer = System.Text.Encoding.ASCII.GetBytes(Server_Command.ToCharArray())
        m_sslStream.Write(m_buffer, 0, m_buffer.Length)
        Dim Server_Reponse As String
        Server_Reponse = Read_Stream2.ReadLine()
        Return Server_Reponse
    End Function
    Private Sub CmdClose_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles CmdClose.Click
        CloseServer()
        CmdClose.Enabled = False
        CmdDownload.Enabled = True
        ret_Val = 0
    End Sub
    Sub getMesgs(ByVal Num_Emails As Integer)
        Cursor = Cursors.WaitCursor
        Dim List_Resp As String
        Dim I As Integer
        For I = 1 To Num_Emails
            List_Resp = Login(m_sslStream, "LIST " & I.ToString)
            ListBox2.Items.Add(List_Resp)
        Next I
        Cursor = Cursors.Default
    End Sub
    Private Sub Button1_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button1.Click
        If ret_Val = 0 Then
            ListBox2.Items.Add("You are not connected, please connect")
            Exit Sub
        End If
        ListBox2.Items.Clear()
        getMesgs(Integer.Parse(server_Stat(1)))
    End Sub
    Sub GetEmails(ByVal Server_Command As String)
        Dim m_buffer() As Byte = System.Text.Encoding.ASCII.GetBytes(Server_Command.ToCharArray())
        Dim stream_Reader As StreamReader
        Dim TxtLine As String = ""
        Try
            m_sslStream.Write(m_buffer, 0, m_buffer.Length)
            stream_Reader = New StreamReader(m_sslStream)
            Do While stream_Reader.Peek() <> -1
                TxtLine += stream_Reader.ReadLine() & vbNewLine
            Loop
            TextBox1.Text = TxtLine
        Catch ex As Exception
            MsgBox(ex.Message)
        End Try
    End Sub
    Private Sub ListBox2_DoubleClick(ByVal sender As Object, ByVal e As System.EventArgs) Handles ListBox2.DoubleClick
        Dim Index_Num As String
        Dim StrRetr As String
        TextBox1.Text = ""
        Try
            Index_Num = (ListBox2.SelectedIndex + 1).ToString
            StrRetr = ("RETR " + Index_Num + vbCrLf)
            GetEmails(StrRetr)

        Catch ex As Exception
            MsgBox(ex.Message)
        End Try
    End Sub
    Private Sub Button2_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button2.Click
        Application.Exit()
    End Sub
End Class
'End here 

Link for update NO. 2 - Here 


This update discusses : 
 

  • How to get a list of all your E-mails from a POP3 server (i.e. Gmail.com)
  • Download and read your E-mails as a text format.
  • Dressing up your application to be more user-friendly.
  • Successfully disconnects from the server and re-login back without any errors. 

Photo for update (2) :   

Final Update : Jan-2013 Fixing issues and source code download.

This update is about displaying the E-mail to read it : I noticed that sometimes the the E-mail won't arrive in full, even with a double click the whole stream package doesn't fully transfered to the TextBox and you get just a part of it, also most of the times (and it depends on the E-mail Server) the request doesn't execute the way it was requested, I.E. if you clicked on E-mail mail message No.1 and then you clicked on Message No.2 you would get the No.1 still. (Download and full description in the Update section below)

Points of Interest   

You will notice that after you try this, you will get response from the gmail server, but :
- You need to be familiar with POP commands, you can find reference here .
- If you are using 2-step verification method in your Gmail account, you will need to create an application password to be able to login from outside Google, here is how!
- Also you may want to consider using outlook as a start if you haven't work before with e-mail clients only to make sure that the service is working fine between you and the server .
- If you had any errors trying this code please post it, i already tried this on all of the MS OSs.  

Problems to be solved later in further updates 

The problem is that in Gmail.com we will retrieve all E-mails from Inbox and all other folders so if you have (22) E-mails in Inbox and (20) in SentBox and (50) in Trash then we will be getting (22+20+50) = 92 E-mails and we won't be able to tell which one is in which Box, but we will come to this later in our project.

Also the E-mails downloaded will be in absolute Text format, so there will be no links or images displayed at the moment, but we will come to this also later.   

How does it work now ?! 

Before I start let me tell you that :

Logout button is [Enabled=False] from properties panel.
TextBox1 for reading E-mails is [ReadOnly=True] and [MultiLine=True] from properties panel.


Now, it goes like this : 

  • Ctrl+F5 The application starts up you will find Logout button is disabled so you can not logout before you Login
  • You click on Login Button, if the info provided are successful then you will receive 3 lines in Server Response ListBox1 as shown in the Photo above.
  • You will then notice that Login Button is disabled and the Logout Button is now enabled.
  • If you choosed to click on Logout Button now you will notice that a 4th line is added to the Server Response ListBox1 [+OK Farewell] and it means that you are now disconnected from the POP3 server. 
  • Clicking on Login Button again will get you back on track and be logged in and also you will find the number of E-mails in the Messages TextBox [MsgCount] .... see update (2) for more information about this number of E-mails .
  • Clicking now on Get E-mails List [Button1] will make the application busy retrieving your E-mails into The ListBox2 and you will be able to see the scrollBar shrinking as a sign of retrieving the Messages.
  • After the List of messages successfully fills the [ListBox2] you can now DoubleClick on any number of this list to read this E-mail in the TextBox1 as absolute Text format which we will be handling it later to be more user friendly.  (Final Update)
  • Clicking on Logout [CmdClose] again will disconnect the server and empty all controls except your loggin settings and disable the Logout Button [CmdClose] and enables the Login Button [CmdDownload] again to start over. 

History  

Link for update NO. 1 - Here  

Link for update NO. 2 - Here   

Link for Final update NO. 3 - Here  

License

This article, along with any associated source code and files, is licensed under The Code Project Open License (CPOL)

About the Author

evry1falls
Software Developer Freelancer
Egypt Egypt
experience in :
MS Visual Studio (0.6 - 2005)
MS Sql Server (2000 - 2003)
MS Access (97 - 2000 - 2003)
PHP/MySql
HTML 5
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Comments and Discussions

 
QuestionWorks great for Gmail BUT PinmemberMember 276043827-Oct-12 22:46 
AnswerRe: Works great for Gmail BUT Pinmemberevry1falls2-Nov-12 10:13 

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