Receiving Email in VB.NET App

[rustyd]

Hi,

 

New to the sockets stuff and I have some questions about attempting to retrieve email via a .NET application. I've read quite a few posts about sending email, but the receiving posts seem to say they have a problem and subsequent posts recommend Email components or they figured it out themselves with no solution.

 

So, here we go a journey to create my own email component.

 

First, using sockets do I connect to my mail server? I've read some posts about listening on port 110. So, I connect to mail server, then listen on port 110. Am I on the right track?

 

Any help is appreciated.

 

Thanks

[PlausiblyDamp]

Other way round, the mail server (if it is POP3) will listen on 110 - you will need to connect to it.

Most of the work involved is simple comands that would be sent / received as simple ASCII text over a connection to port 110.

[rustyd]

Found a C# example and converted to VB.NET

 

I found a C# example and converted to VB.NET.

 

I can't get it to connect to my mail server. The Connect(mailsite, 110) doesn't error out, but when I get the response I get the error:

Operation not allowed on non-connected sockets

 

I have a form with 3 textboxes (mailserver, user,pass) and a button that

when clicked calls a routine GetMail. GetMail creates and instance of my

Pop3 class which inherits Net.Sockets.TcpClient and I call the overloaded

function Connect(mailserver, 110). Once the Connect call is made it returns

and I call Response() which uses the NetworkStream object and GetStream().

This is where the error occurs. I've include the exact error message and the entire Pop3 class.

 

Here is the exact error message:

 

System.InvalidOperationException: Operation not allowed on non-connected sockets.
  at System.Net.Sockets.TcpClient.GetStream()
  at TestMail.Pop3.Response() in C:\Documents and Settings\Rusty\My Documents\Visual Studio Projects\TestMail\Pop3.vb:line 141
  at TestMail.Pop3.Connect(String server, String username, String password) in C:\Documents and Settings\Rusty\My Documents\Visual Studio Projects\TestMail\Pop3.vb:line 13
  at TestMail.Form1.GetMail() in C:\Documents and Settings\Rusty\My Documents\Visual Studio Projects\TestMail\Form1.vb:line 130

 

Here is my class:

Public Class Pop3
 Inherits System.Net.Sockets.TcpClient

 Public Overloads Sub Connect(ByVal server As String, ByVal username As String, ByVal password As String)

   Dim message As String
   Dim response1 As String
   Dim x As New Net.Sockets.TcpClient()

   x.Connect(server, 110)
   response1 = Response()

   If (response1.Substring(0, 3) <> "+OK") Then
     Dim Pop3Ex As Pop3Exception
     Pop3Ex.Pop3Exception(response1)
   End If

   message = "USER " + username + vbCrLf
   Write(message)
   response1 = Response()
   If (response1.Substring(0, 3) <> "+OK") Then
     Dim Pop3Ex As Pop3Exception
     Pop3Ex.Pop3Exception(response1)
   End If

   message = "PASS " + password + vbCrLf
   Write(message)
   response1 = Response()
   If (response1.Substring(0, 3) <> "+OK") Then
     Dim Pop3Ex As Pop3Exception
     Pop3Ex.Pop3Exception(response1)
   End If
 End Sub

 Public Sub Disconnect()
   Dim message As String
   Dim response1 As String

   message = "QUIT" & vbCrLf
   Write(message)
   response1 = Response()
   If (response1.Substring(0, 3) <> "+OK") Then
     Dim Pop3Ex As Pop3Exception
     Pop3Ex.Pop3Exception(response1)
   End If
 End Sub

 Public Function List() As ArrayList

   Dim message As String
   Dim response1 As String

   Dim retval As New ArrayList()

   message = "LIST" & vbCrLf
   Write(message)
   response1 = Response()
   If (response1.Substring(0, 3) <> "+OK") Then
     Dim Pop3Ex As Pop3Exception
     Pop3Ex.Pop3Exception(response1)
   End If

   Do While (True)
     response1 = Response()
     If (response1 = "." & vbCrLf) Then
       Return retval
     Else
       Dim msg = New Pop3Message()
       Dim seps As Char = "' '"
       Dim values() As String = response1.Split(seps)

       msg.number = Int32.Parse(values(0))
       msg.bytes = Int32.Parse(values(1))
       msg.retrieved = False
       retval.Add(msg)
       'continue()
     End If
   Loop
 End Function

 Public Function Retrieve(ByVal rhs As Pop3Message) As Pop3Message
   Dim message As String
   Dim response1 As String

   Dim msg = New Pop3Message()
   msg.bytes = rhs.bytes
   msg.number = rhs.number

   message = "RETR " + rhs.number + vbCrLf
   Write(message)
   response1 = Response()
   If (response1.Substring(0, 3) <> "+OK") Then
     Dim Pop3Ex As Pop3Exception
     Pop3Ex.Pop3Exception(response1)
   End If

   msg.retrieved = True
   Do While (True)
     response1 = Response()
     If (response1 = "." & vbCrLf) Then
       Exit Do
     Else
       msg.message += Response()
     End If
   Loop

   Return msg
 End Function

 Public Sub Delete(ByVal rhs As Pop3Message)
   Dim message As String
   Dim response1 As String

   message = "DELE " + rhs.number + vbCrLf
   Write(message)
   response1 = Response()
   If (response1.Substring(0, 3) <> "+OK") Then
     Dim Pop3Ex As Pop3Exception
     Pop3Ex.Pop3Exception(response1)
   End If
 End Sub

 Private Sub Write(ByVal message As String)
   Dim en = New System.Text.ASCIIEncoding()

   Dim WriteBuffer(1024) As Byte
   WriteBuffer = en.GetBytes(message)

   Dim stream As Net.Sockets.NetworkStream
   stream.Write(WriteBuffer, 0, WriteBuffer.Length)

   Debug.WriteLine("WRITE:" + message)
 End Sub

 Private Function Response() As String
   Dim enc = New System.Text.ASCIIEncoding()
   Dim serverbuff(1024) As Byte
' **********************
' ERROR OCCURS ON THIS LINE
   Dim stream As Net.Sockets.NetworkStream = GetStream()

   Dim count As Integer = 0
   Do While (True)
     Dim buff(2) As Byte
     Dim bytes As Integer = stream.Read(buff, 0, 1)
     If (bytes = 1) Then
       serverbuff(count) = buff(0)
       count += 1
       If (buff(0) = vbLf) Then
         Exit Do
       End If
     Else
       Exit Do
     End If
   Loop

   Dim retval As String = enc.GetString(serverbuff, 0, count)
   Debug.WriteLine("READ:" + retval)
   Return retval
 End Function
End Class

Edited March 31, 2005 by rustyd

[Mister E]

It sounds like you're not connected to the server. I would get rid of everything else and concentrate on establishing a TCP connection with the mail server first. Once you have that you can gradually add functionality and test things incrementally. A good way to practice POP3 commands is to telnet into the mail server and then send the commands by typing them in by hand on your telnet client. The remote mail server should respond and send you back some ASCII characters containing the email header, body, and other things. This will give you an idea of how the information is flowing and will allow you to better understand the process of handling the raw bytes for the connection. I believe RFC 1939 is the one that lists the POP3 specification.

[rustyd]

Telnet vs. My app

 

I can connect successfully via telnet with the command:

open mymailserver 110

 

responds with:

+OK Hello There!

 

I overload the connect method in my Pop3 class and use:

Connect(mailserver, 110)

 

I get the error:

Operation not allowed on non-connected sockets

 

I change the Connect to:

 

Connect("open " + mailserver, 110)

 

I get the error:

System.Net.Sockets.SocketException: The requested name is valid and was

found in the database, but it does not have the correct associated data

being resolved

 

What do you make of this?

[rustyd]

On to the next problem

 

Wanted to report that I remembered reading a post about someone having problems with their sockets program and they were told about mscorcfg.exe to setup permissions for the program.

 

I added TestMail.exe to the applications and I can connect!!

 

OK, enough of the good news. Now I have problems in the Response() call. It crashes on the line

 

If (buff(0) = vbLf) Then

 

I'm comparing a byte to a string. So, I'll get this figured out. Thanks for your help so far.

[rustyd]

Yeah!! Got it to connect.

 

Fixed the Response() function. Now onto getting it to pull emails.