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ivan  
#1 Posted : Monday, May 2, 2011 5:13:19 PM(UTC)
ivan

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VB6 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

Option Explicit 

Const MailServerPop3 = 0 
Const MailServerImap4 = 1 

Private m_uidlfile As String 
Private m_uidls As String 

Private oTools As New EAGetMailObjLib.Tools 

'==========================================================================================
' 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 Sub LoadUIDL() 
    m_uidls = "" 
    m_uidls = oTools.ReadTextFile(m_uidlfile, 0) 
End Sub 

Private Sub UpdateUIDL() 
    On Error GoTo ErrorHandleUpdateUIDL 
    oTools.WriteTextFile m_uidlfile, m_uidls, 0 
    On Error GoTo 0 
    Exit Sub 
ErrorHandleUpdateUIDL: 
    MsgBox "Update UIDL Error: " & Err.Description 
    On Error GoTo 0 
End Sub 

Private Sub SyncUIDL(ByRef oServer As EAGetMailObjLib.MailServer, ByRef infos) 
    Dim arLocal 
    Dim newuidls As String 
    Dim uidlpref As String 
    uidlpref = LCase(oServer.Server) & "#" & LCase(oServer.User) & " " 

    arLocal = Split(m_uidls, vbCrLf) 
    Dim i, Count 
    For i = LBound(arLocal) To UBound(arLocal) 
        Dim t As String 
        Dim bRemove As Boolean 
        bRemove = False 
        t = arLocal(i) 
        If Len(t) > Len(uidlpref) Then 
            Dim curPref 
            curPref = Left(t, Len(uidlpref)) 
            If StrComp(curPref, uidlpref, vbBinaryCompare) = 0 Then 

                Dim localuidl 
                localuidl = Mid(t, Len(uidlpref) + 1) 

                Dim bExistOnServer As Boolean 
                bExistOnServer = False 

                Dim x 
                For x = LBound(infos) To UBound(infos) 
                    If StrComp(infos(x).UIDL, localuidl, vbBinaryCompare) = 0 Then 
                        bExistOnServer = True 
                    Exit For 
                    End If 
                Next 
                If Not bExistOnServer Then 
                    bRemove = True 
                End If 
            End If 
        End If 

        If Trim(t) = "" Then 
            bRemove = True 
        End If 

        If Not bRemove Then 
            newuidls = newuidls & t & vbCrLf 
        End If 
    Next 

    m_uidls = newuidls 
End Sub 

Private Function FindExistedUIDL(ByRef oServer As EAGetMailObjLib.MailServer, _ 
        ByRef UIDL As String) As Boolean 
        Dim s As String 
        s = LCase(oServer.Server) & "#" & LCase(oServer.User) & " " & UIDL & vbCrLf 
        If InStr(1, m_uidls, s, vbBinaryCompare) > 0 Then 
            FindExistedUIDL = True 
        Else 
            FindExistedUIDL = False 
        End If 
End Function 

Private Sub AddUIDL(ByRef oServer As EAGetMailObjLib.MailServer, ByRef UIDL As String) 
        Dim s As String 
        s = LCase(oServer.Server) & "#" & LCase(oServer.User) & " " & UIDL & vbCrLf 
        m_uidls = m_uidls & s 
End Sub 

Private Sub Command1_Click() 
    Dim curpath As String 
    Dim mailbox As String 

    ' Create a folder named "inbox" under current directory
    ' to save the email retrieved.
    curpath = App.Path 
    mailbox = curpath & "\inbox" 
    m_uidlfile = curpath & "\uidl.txt" 
    oTools.CreateFolder mailbox 

    Dim oServer As New EAGetMailObjLib.MailServer 
    oServer.Server = "pop3.emailarchitect.net" 
    oServer.User = "test@emailarchitect.net" 
    oServer.Password = "testpassword" 
    oServer.Protocol = MailServerPop3 

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

    On Error GoTo ErrorHandle: 
    Dim oClient As New EAGetMailObjLib.MailClient 
    oClient.LicenseCode = "TryIt" 

    oClient.Connect oServer 
    MsgBox "Connected" 

    ' 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 infos 
    infos = oClient.GetMailInfos() 
    MsgBox UBound(infos) + 1 & " emails" 

    SyncUIDL oServer, infos 

    Dim i As Integer 
    For i = LBound(infos) To UBound(infos) 
        Dim info As EAGetMailObjLib.MailInfo 
        Set info = infos(i) 
        MsgBox "Index: " & info.Index & "; Size: " & info.Size & _ 
        "; UIDL: " & info.UIDL 

        ' If this email has not been downloaded before, then get it
        If Not FindExistedUIDL(oServer, info.UIDL) Then 

            ' Receive email from POP3 server
            Dim oMail As EAGetMailObjLib.Mail 
            Set oMail = oClient.GetMail(info) 

            MsgBox "From: " & oMail.From.Address & _ 
                vbCrLf & "Subject: " & oMail.Subject 

            Dim fileName As String 
            ' Generate a random file name by current local datetime,
            ' You can use your method to generate the filename if you do not like it
            fileName = mailbox & "\" & oTools.GenFileName(i) & ".eml 

            ' Save email to local disk
            oMail.SaveAs fileName, True 

            ' Add the email uidl to uidl file to avoid we retrieve it next time.
            AddUIDL oServer, info.UIDL 
            ' Do not delete the email
        End If 
    Next 

    ' Quit
    oClient.Quit 

    ' Update the uidl list to a text file and then we can load it next time.
    UpdateUIDL 
    Exit Sub 

ErrorHandle: 
    MsgBox Err.Description 
    ' Update the uidl list to a text file and then we can load it next time.
    UpdateUIDL 
End Sub 

Click here to read original topic - full version ...

If you have any comments or questions about above example codes, please add your comments here.
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