Implement POP3 and SMTP in .NET

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Introduction

This article shows how to use VB.NET to implement POP3 and SMTP protocol. There is a DLL file included in the source files, this DLL contains two classes to implement POP3 and SMTP and an extra class for e-mail's codec (base 64 only, not included in the source code because it is being tested now).

Any questions? Please contract me immediately at soldierq@msn.com.

Main functions in these Classes

The most basic functions are the same in POP3 class and the SMTP class.

Connect to Mail Server

Private Function Connect() As Boolean
     Try
         sockPOP3.Connect(m_Remote)

         If sockPOP3.Connected = True Then
             sockPOP3.Receive(bufferReceive)
             Return True
         Else
             Return False
         End If
     Catch ex As Exception
         sockPOP3.Close()
         Throw New Exception("Failed to Connect " +
                     "Host:" & vbCrLf & ex.Message)
     End Try
 End Function

Send Commands to Server

Private Function SendCommand(ByVal Command As String) As Byte()
    Try
        bufferSend = Encoding.ASCII.GetBytes(Command & vbCrLf)
        sockPOP3.Send(bufferSend)


        Array.Clear(bufferReceive, 0, bufferReceive.Length)
        sockPOP3.Receive(bufferReceive)

        Return bufferReceive
    Catch ex As Exception
        Throw New Exception("Error In Sending " +
           "Command To Server:" & vbCrLf & ex.Message)
    End Try
End Function

Check Server Response

'POP3
'The pop3 server will return "+OK" when command success, 
'otherwise it will return "-ERR".
    Private Function CorrectedResponse(ByVal ReceivedBytes() As Byte, _
                        Optional ByRef Message As String = "") As Boolean
        Dim strText As String = Encoding.ASCII.GetString(ReceivedBytes)
        Message = strText
        RaiseEvent GotResponse(strText)
        If strText.StartsWith("+OK") Then
            Return True
        Else
            Return False
        End If
    End Function
'SMTP
'The SMTP server will return a message with a three-bit-digital 
'for each command. The first bit indicates whether the 
'command is successful or failed as show below

    Private Function CorrectedResponse(ByVal ReceivedBytes() As Byte, _
                       Optional ByRef Message As String = "") As Boolean
        'The first digital of the three digitals in 
        'response message indicates as follow:
        '1: command accepted, waiting for confirm
        '2: command executed
        '3: command accepted, waiting for more information
        '4: command refused
        '5: command failed
        Dim strText As String = Encoding.ASCII.GetString(ReceivedBytes)
        Message = strText
        RaiseEvent GotResponse(strText)
        Select Case strText.Substring(0, 1)
            Case 1, 2, 3
                Return True
            Case 4, 5
                Return False
            Case Else
                Return False
        End Select
    End Function

Commands in POP3 and SMTP

Here I'll just show you two session samples with a mail server using Microsoft Exchange. The mail class calls the SendCommand() method and the CorrectedResponse() method to send commands to the server and check the command execution results. You can find more information about the POP3 and SMTP protocol standards on the Web.

The bold string indicates it's a command:

==SMTP===
220 Microsoft ESMTP MAIL Service, Version: 5.0.2195.6713 ready at 
Fri, 13 Aug 2004 11:12:22 +0800 
helo 
250 mail.cyberrs2.com Hello [192.168.101.52] 
mail from:test@test.com 
250 2.1.0 test@test.com ....Sender OK 
rcpt to:abc@abc.com 
250 2.1.5 abc@abc.com 
data 
354 Start mail input; end with <CRLF>.<CRLF> 
subject:test test smtp & pop3 
. 
250 2.6.0 <MAILiAXL21xDenYPnDd00022f02> Queued mail for delivery 
quit 
221 2.0.0 Service closing transmission channel
==POP3==
+OK Microsoft Exchange Server 2003 POP3 6.5.6944.0 (mail.cyberrs2.com)
user test
+OK 
pass ****** 
+OK User successfully logged on. 
stat 
+OK 1 414 
list
+OK 1 414 
1 414 
. 
retr 1 
+OK 
Received: Microsoft SMTPSVC(5 .0.2195.6713); 
Fri, 13 Aug 2004 11:12:45 +0800 subject:test From: test@test.com
Bcc: 
Return-Path: test@test.com
Message-ID: <MAILiAXL21xDenYPnDd00022f02> 
X-OriginalArrivalTime: 13 Aug 2004 03:13:00.0356 (UTC) 
FILETIME=[7051D840:01C480 E3]
Date: 13 Aug 2004 11:13:00 +0800 
test smtp & pop3 
.
dele 1 
+OK 
quit 
+OK Microsoft Exchange Server 2003 POP3 6.5.6944.0

How to use the QMailClient Class

'Get mail list from serverrDim MailReceiver As QMailClient.POP3Client
MailReceiver = New POP3Client        
MailReceiver.RemoteServerAddress = "pop3.163.com"
MailReceiver.UserName = "xxx"
MailReceiver.Password = "yyyy"
'Optional, please set this TRUE when you are under firewall or 
'using antivirus software which will scan incoming and outgoing mails.
MailReceiver.IncreaseNetworkCompatible = True  
If MailReceiver.Login() = False Then
  MessageBox.Show("Login failed", "Error", _
     MessageBoxButtons.OK, MessageBoxIcon.Error)
  Exit Sub
End If

If Not arrList Is Nothing Then
  arrList.Clear()
  arrList = MailReceiver.GetMailList(True)
  MailReceiver.Quit()
End Iff
'Get a mail from server according to the 
'mail index which can be obtained in mail list
Dim MailReceiver As QMailClient.POP3Client
MailReceiver = New POP3Client
MailReceiver.RemoteServerAddress = "pop3.163.com"
MailReceiver.UserName = "xxx"
MailReceiver.Password = "yyyy"
MailReceiver.IncreaseNetworkCompatible = True  
Try
  MailReceiver.Login()
  'Mail Index, it can be obtain from mail list(start from 1)
  Mail = MailReceiver.RetrieveMail(MailIndex)   
Catch ex As Exception
  MessageBox.Show(ex.Message, "Error", _
       MessageBoxButtons.OK, MessageBoxIcon.Error)
Finally
  MailReceiver.Quit()


End Try
'NOTES: The Retrievemail() method has two overloads which will return 
'a QMailClient.EMail object or the source code string of the mail,
'The EMail object can decode the mail automatically and 
'support many mail content type such as multipart/mixed,
'multipart/related and multipart/report.
'If you want to use your own mail decoder then just call the overload 
'function which only return mail source code (string).
'Show mail on a form or a web page
'NOTES: The code below is not assured to run because it needs some 
'form controls, here just show an example.
'The Email.body contains the plain text mail content and the 
'Email.bodyHTML contains the source HTML code of the mail 
'content if the mail is formatted in HTML
    Private Sub ShowMail()
>>        Me.lblMailDate.Text = "DATE: " & Mail.Date
>>        Me.lblMailFrom.Text = "FROM: " & Mail.From
>>        Me.lblMailSubject.Text = "SUBJECT: " & Mail.Subject
>>        Me.lblMailTo.Text = "TO: " & Mail.To
>>        'Write a temp file to show HTML mail
>>        If Mail.BodyContentType = EMail.ContentType.MultipartAlternative Then
>>            Dim file As New FileStream(FolderTmp & "tmp.html", _
                             FileMode.Create, FileAccess.Write, FileShare.None)
>>            Dim a As Encoding = Encoding.GetEncoding("gb2312")
>>
>>            file.Write(a.GetBytes(Mail.BodyHTML), 0, _
                                         a.GetByteCount(Mail.BodyHTML))
>>            file.Close()
>>            Me.rtxtContent.Text = Mail.Body
>>            Me.tbtnHTML.Enabled = True
>>        ElseIf Mail.BodyContentType = EMail.ContentType.MultipartRelated Then
>>            Dim file As New FileStream(FolderTmp & "tmp.html", _
                          FileMode.Create, FileAccess.Write, FileShare.None)
>>            Dim a As Encoding = Encoding.GetEncoding("gb2312")
>>
>>            Dim att As MailAttachment
>>            Dim strBody As String = Mail.BodyHTML
>>            For Each att In Mail.Attachments
>>                If att.ContentID <> "" Then
>>                    strBody = strBody.Replace("cid:" & att.ContentID, _
                                                            att.FileName)
>>                    att.SaveToFile(FolderTmp & att.FileName)
>>                End If
>>            Next
>>
>>            file.Write(a.GetBytes(strBody), 0, a.GetByteCount(strBody))
>>            file.Close()
>>            Me.rtxtContent.Text = Mail.Body
>>            Me.tbtnHTML.Enabled = True
>>        Else
>>            Me.rtxtContent.Text = Mail.Body
>>            Me.tbtnHTML.Enabled = False
>>        End If
>>
>>        If Mail.Attachments.Count <> 0 Then
>>            Dim mailAttach As MailAttachment
>>
>>            For Each mailAttach In Mail.Attachments
>>                'Create a empty file in order to get icon
>>                Dim strExName As String = _
>>                   FileInformation.GetFileExtendedName(mailAttach.FileName)
>>                Dim strmFile As New _
>>                   FileStream(FolderTmp & "ico." & strExName, _
>>                                                          FileMode.Create)
>>                strmFile.Close()
>>
>>                Dim fsi As System.IO.FileSystemInfo
>>                fsi = New FileInfo(FolderTmp & "ico." & strExName)
>>                imgFileIcons.Images.Add(IconExtractor.GetSmallIcon(fsi))
>>                lstvAttachments.Items.Add(_
                            SysInfomation.GetFileNameFromFilePath(_
                                               mailAttach.FileName), _
                                               imgFileIcons.Images.Count - 1)
>>            Next
>>            Me.grpbxAttach.Visible = True
>>        End If
>>    End Sub
'Sending a mail
>>>>       Dim mailSend As New QMailClient.EMail
                       'Use ";" to splite multi-receivers
>>>>       mailSend.To = "abc@bcd.com;dd@dd.com"   
>>>>       mailSend.Cc = "cc@dd.com"
>>>>       mailSend.Subject = "test"
>>>>       mailSend.Body = "test1"
>>>>       mailSend.From = "abc@abc.com"
>>>>              
>>>>       Dim mailClient As New SMTPClient
>>>>       mailClient.RemoteServerAddress = "pop3.163.com"
>>>>             
>>>>       mailClient.IncreaseNetworkCompatible = True
>>>>
>>>>       If mailClient.Connect = True Then
>>>>                    
>>>>           mailClient.UserName = "user"
>>>>           mailClient.Password = "pass"
>>>>                      
>>>>           If mailClient.AuthLogin = False Then
>>>>               MessageBox.Show("Authentication failed", _
                                   "Error", MessageBoxButtons.OK, _
                                              MessageBoxIcon.Error)
>>>>                            
>>>>               Exit Sub
>>>>           End If
>>>>               
>>>>                   
>>>>           mailClient.SendMail(mailSend)
>>>>          
>>>>           mailClient.Quit()
>>>>
>>>>           mailClient = Nothing
>>>>       End If