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ivan  
#1 Posted : Tuesday, April 12, 2011 5:10:50 AM(UTC)
ivan

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Visual Basic.NET Example

If you want to leave a copy of email on the server, you should not call Delete method. However, there is a problem, how can you know if the email has already been downloaded (read)? If there is a way to identify the downloaded email, you can avoid downloading the duplicated email from your POP3/IMAP4 server.

Every email has a unique identifier (UIDL) on POP3 server. POP3 UIDL is only unique in the email life time. That means if the email was deleted from the server, other email can use the old unique identifier. Another problem is: UIDL in POP3 server can be any number or characters, so we cannot use UIDL as the file name, because UIDL may contain invalid characters for file name.

To solve this problem, we have to store the UIDL to a txt file and synchronize it with server every time.

The following example codes demonstrate how to mark the email as downloaded/read on POP3 server.

Code:

' The following example codes demonstrate marking email as read/downloaded on POP3 server
' To get full sample projects, please download and install EAGetMail on your machine.
' To run it correctly, please change email server, user, password, folder, file name value to yours

Imports System.Collections 
Imports System.Text 
Imports System.IO 

' Imports EAGetMail namespace
Imports EAGetMail 

Module Module1 
    Public Class MyMailClient 
        Private m_arUidl As ArrayList = New ArrayList 
        Private m_uidlfile As String = "uidl.txt" 
        Private m_curpath As String = "" 
#Region "UIDL Functions" 
        ' Uidl is the identifier of every email on POP3/IMAP4 server, to avoid
        ' retrieve the same email from server more than once, we record the
        ' email uidl retrieved every time if you delete the email from server
        ' every time and not to leave a copy of email on the server, then please
        ' remove all the function about uidl.
        Private Function _FindUIDL(ByVal infos() As MailInfo, ByVal uidl As String) As Boolean 
            Dim count As Integer = infos.Length 
            For i As Integer = 0 To count - 1 
                If String.Compare(infos(i).UIDL, uidl, False) = 0 Then 
                    _FindUIDL = True 
                    Exit Function 
                End If 
            Next 
            _FindUIDL = False 
        End Function 

        ' Remove the local uidl which is not existed on the server.
        Private Sub _SyncUIDL(ByVal oServer As MailServer, ByVal infos() As MailInfo) 
            Dim s As String = String.Format("{0}#{1} ", oServer.Server, oServer.User) 
            Dim bcontinue As Boolean = False 
            Dim n As Integer = 0 

            Do 
                bcontinue = False 
                Dim count As Integer = m_arUidl.Count 
                For i As Integer = n To count - 1 
                    Dim x As String = m_arUidl(i) 
                    If String.Compare(s, 0, x, 0, s.Length, True) = 0 Then 

                        Dim pos As Integer = x.LastIndexOf(" ") 
                        If pos <> -1 Then 
                            Dim uidl As String = x.Substring(pos + 1) 
                            If (Not _FindUIDL(infos, uidl)) Then 

                                ' this uidl doesn't exist on server,
                                ' we should remove it from local uidl list.
                                bcontinue = True 
                                n = i 
                                m_arUidl.RemoveAt(i) 
                                Exit For 
                            End If 
                        End If 
                    End If 
                Next 
            Loop While (bcontinue) 

        End Sub 

        Private Function _FindExistedUIDL(ByVal oServer As MailServer, _ 
                ByVal uidl As String) As Boolean 
            Dim s As String = String.Format("{0}#{1} {2}", _ 
                oServer.Server.ToLower(), oServer.User.ToLower(), uidl) 
            Dim count As Integer = m_arUidl.Count 
            For i As Integer = 0 To count - 1 
                Dim x As String = m_arUidl(i) 
                If String.Compare(s, x, False) = 0 Then 
                    _FindExistedUIDL = True 
                    Exit Function 
                End If 
            Next 
            _FindExistedUIDL = False 
        End Function 

        Private Sub _AddUIDL(ByVal oServer As MailServer, ByVal uidl As String) 
            Dim s As String = String.Format("{0}#{1} {2}", _ 
                 oServer.Server.ToLower(), oServer.User.ToLower(), uidl) 
            m_arUidl.Add(s) 
        End Sub 

        Private Sub _UpdateUIDL() 
            Dim s As New StringBuilder 
            Dim count As Integer = m_arUidl.Count 
            For i As Integer = 0 To count - 1 
                s.Append(m_arUidl(i)) 
                s.Append(vbCrLf) 
            Next 

            Dim file As String = String.Format("{0}\{1}", m_curpath, m_uidlfile) 
            Dim fs As FileStream = Nothing 

            Try 
                fs = New FileStream(file, FileMode.Create, FileAccess.Write, FileShare.None) 
                Dim data() As Byte = System.Text.Encoding.Default.GetBytes(s.ToString()) 
                fs.Write(data, 0, data.Length) 
                fs.Close() 
            Catch ep As Exception 
                If Not (fs Is Nothing) Then 
                    fs.Close() 
                End If 
                Throw ep 
            End Try 
        End Sub 

        Private Sub _LoadUIDL() 

            m_arUidl.Clear() 
            Dim filename As String = String.Format("{0}\{1}", m_curpath, m_uidlfile) 
            Dim read As StreamReader = Nothing 

            Try 
                read = File.OpenText(filename) 
                Do While (True) 
                    Dim line As String = read.ReadLine().Trim(vbCrLf & " " & vbTab.ToCharArray()) 
                    m_arUidl.Add(line) 
                Loop 
            Catch ep As Exception 
            End Try 

            If Not (read Is Nothing) Then 
                read.Close() 
            End If 
        End Sub 
#End Region 

        Public Sub ReceiveEmail(ByVal oServer As MailServer, ByVal bLeaveCopy As Boolean) 
            Dim oClient As New MailClient("TryIt") 
            m_curpath = Directory.GetCurrentDirectory() 
            Try 
                ' Uidl is the identifier of every email on POP3/IMAP4 server, to
                ' avoid retrieve the same email from server more than once,
                ' we record the email uidl retrieved every time if you delete the
                ' email from server every time and not to leave a copy of email on
                ' the server, then please remove all the function about uidl.
                _LoadUIDL() 

                Dim mailFolder As String = [String].Format("{0}\inbox", m_curpath) 
                If Not Directory.Exists(mailFolder) Then 
                    Directory.CreateDirectory(mailFolder) 
                End If 

                Console.WriteLine("Connecting server ... ") 
                oClient.Connect(oServer) 
                Dim infos As MailInfo() = oClient.GetMailInfos() 
                Console.WriteLine("Total {0} email(s)", infos.Length) 

                _SyncUIDL(oServer, infos) 
                Dim count As Integer = infos.Length 

                For i As Integer = 0 To count - 1 
                    Dim info As MailInfo = infos(i) 
                    If _FindExistedUIDL(oServer, info.UIDL) Then 
                        ' this email has existed on local disk.
                        Continue For 
                    End If 

                    Console.WriteLine("Retrieving {0}/{1}...", info.Index, count) 

                    Dim oMail As Mail = oClient.GetMail(info) 
                    Dim d As System.DateTime = System.DateTime.Now 
                    Dim cur As New System.Globalization.CultureInfo("en-US") 
                    Dim sdate As String = d.ToString("yyyyMMddHHmmss", cur) 
                    Dim fileName As String = [String].Format("{0}\{1}{2}{3}.eml", _ 
                         mailFolder, sdate, d.Millisecond.ToString("d3"), i) 
                    oMail.SaveAs(fileName, True) 

                    If bLeaveCopy Then 

                        ' Add the email uidl to uidl file to avoid we retrieve it next time.
                        _AddUIDL(oServer, info.UIDL) 
                    End If 
                Next 

                If Not bLeaveCopy Then 
                    Console.WriteLine("Deleting ...") 
                    For i As Integer = 0 To count - 1 
                        oClient.Delete(infos(i)) 
                    Next 
                End If 

                Console.WriteLine("Completed") 
                oClient.Quit() 
            Catch ep As Exception 
                Console.WriteLine(ep.Message) 
            End Try 

            ' Update the uidl list to a text file and then we can load it next time.
            _UpdateUIDL() 
        End Sub 
    End Class 

    Sub Main() 
        ' Create a folder named "inbox" under current directory
        ' to save the email retrieved.
        Dim curpath As String = Directory.GetCurrentDirectory() 
        Dim mailbox As String = [String].Format("{0}\inbox", curpath) 

        ' If the folder is not existed, create it.
        If Not Directory.Exists(mailbox) Then 
            Directory.CreateDirectory(mailbox) 
        End If 

        Dim oServer As New MailServer("pop3.emailarchitect.net", _ 
            "test@emailarchitect.net", "testpassword", ServerProtocol.Pop3) 
        Dim oClient As New MailClient("TryIt") 

        ' If your POP3 server requires SSL connection,
        ' Please add the following codes:
        ' oServer.SSLConnection = True
        ' oServer.Port = 995

        Dim MyClient As New MyMailClient 
        MyClient.ReceiveEmail(oServer, True) 

    End Sub 
End Module 


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