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Using UIDL Function to Mark the Email has been downloaded/read in VB 6.0

In previous section, I introduced how to use event handler. In this section, I will introduce how to use UIDL function to mark the email has been downloaded in VB 6.0.

Introduction

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? If there is a way to identify the downloaded email, you can avoid downloading the duplicated email from your POP3/IMAP4 server.

Note

Remarks: All of examples in this section are based on first section: A simple VB 6.0 project. To compile and run the following example codes successfully, please click here to learn how to create the test project and add reference to your project.

[VB 6.0 Example - IMAP4 Solution]

Every email has a unique identifier (UIDL) on IMAP4 server. It is a 32bit integer and it is always unique in your email account life time. So we can use the integer as file name to identify if the email has been downloaded. In order to run it correctly, please change email server, user, password, folder, file name values.

Option Explicit

Const MailServerPop3 = 0
Const MailServerImap4 = 1
Const MailServerEWS = 2
Const MailServerDAV = 3
Const MailServerMsGraph = 4

Private Sub Command1_Click()
    Dim currentPath As String
    Dim localInbox As String
    Dim oTools As New EAGetMailObjLib.Tools

    ' Create a folder named "inbox" under current directory
    ' to save the email retrieved.
    currentPath = App.Path
    localInbox = currentPath & "\inbox"
    oTools.CreateFolder localInbox

    Dim oServer As New EAGetMailObjLib.MailServer
    oServer.Server = "imap4.emailarchitect.net"
    oServer.User = "test@emailarchitect.net"
    oServer.Password = "testpassword"
    oServer.Protocol = MailServerImap4

    ' Enable SSL/TLS connection, most modern email servers require SSL/TLS by default
    oServer.SSLConnection = True
    oServer.Port = 993

    ' If your IMAP doesn't deploy SSL connection
    ' Please use
    ' oServer.SSLConnection = False
    ' oServer.Port = 143

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

    oClient.Connect oServer
    MsgBox "Connected"

    Dim infos As EAGetMailObjLib.MailInfoCollection
    Set infos = oClient.GetMailInfoList()
    MsgBox infos.Count & " emails"

    Dim i As Long
    For i = 0 To infos.Count - 1
        Dim info As EAGetMailObjLib.MailInfo
        Set info = infos.Item(i)

        MsgBox "Index: " & info.Index & "; Size: " & info.Size & _
        "; UIDL: " & info.UIDL

        Dim fileName As String

        ' Using IMAP UIDL as the file name.
        fileName = localInbox & "\" & info.UIDL & ".eml"
        If oTools.ExistFile(fileName) Then
            ' This email has been downloaded, do not receive it again.
        Else

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

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

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

        ' Do not delete email from IMAP4 server.
    Next

    ' Quit and expunge emails marked as deleted from IMAP4 server.
    oClient.Quit
    Exit Sub

ErrorHandle:
    MsgBox Err.Description
End Sub

POP3/IMAP4/Exchange Web Service/WebDAV Solution

There is a little bit different in POP3 server. The 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.

UIDL is also unique in Exchange Web Service/WebDAV, but the UIDL is string but not integer. UIDL in Exchange server may contain invalid characters for file name, so we cannot use UIDL as the file name either.

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

Please have a look at the following example code. It works with both POP3/IMAP4/Exchange Web Service/WebDAV protocol.

Option Explicit

Const MailServerPop3 = 0
Const MailServerImap4 = 1
Const MailServerEWS = 2
Const MailServerDAV = 3
Const MailServerMsGraph = 4

Private oTools As New EAGetMailObjLib.Tools

Private Sub Command1_Click()
    Dim currentPath As String
    Dim localInbox As String
    Dim isUidlLoaded As Boolean

    isUidlLoaded = False

    ' Create a folder named "inbox" under current directory
    ' to save the email retrieved.
    currentPath = App.Path
    localInbox = currentPath & "\inbox"

    oTools.CreateFolder localInbox

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

    ' Enable SSL/TLS connection, most modern email servers require SSL/TLS by default
    oServer.SSLConnection = True
    oServer.Port = 995

    ' If your POP3 doesn't deploy SSL connection
    ' Please use
    ' oServer.SSLConnection = False
    ' oServer.Port = 110

On Error GoTo ErrorHandle:
    Dim leaveCopy As Boolean
    leaveCopy = True

    ' 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.
    ' If you want to re-download all emails, please delete uidl.txt from local inbox.
    Dim oUIDLManager As New EAGetMailObjLib.UIDLManager
    oUIDLManager.Load localInbox & "\uidl.txt"
    isUidlLoaded = True

    Dim oClient As New EAGetMailObjLib.MailClient
    oClient.LicenseCode = "TryIt"

    oClient.Connect oServer
    MsgBox "Connected"

    Dim infos As EAGetMailObjLib.MailInfoCollection
    Set infos = oClient.GetMailInfoList()

    MsgBox infos.Count & " emails"

    ' Remove the local uidl that is not existed on the server,
    oUIDLManager.SyncUIDLEX oServer, infos
    ' Update result back to uidl file
    oUIDLManager.Update

    Dim i As Long
    For i = 0 To infos.Count - 1
        Dim info As EAGetMailObjLib.MailInfo
        Set info = infos.Item(i)

        MsgBox "Index: " & info.Index & "; Size: " & info.Size & _
        "; UIDL: " & info.UIDL

        Dim oUIDLItem As UIDLItem
        Set oUIDLItem = oUIDLManager.FindUIDL(oServer, info.UIDL)

        ' If this email has not been retrieved before, then get it
        If oUIDLItem Is Nothing Then

            Dim fileName As String
            fileName = oTools.GenFileName(i) & ".eml"

            Dim fullFileName As String
            fullFileName = localInbox & "\" & fileName

            Dim oMail As EAGetMailObjLib.Mail
            Set oMail = oClient.GetMail(info)
            oMail.SaveAs fullFileName, True

            If leaveCopy Then
                ' Add the email uidl to uidl file to avoid we retrieve it next time.
                oUIDLManager.AddUIDL oServer, info.UIDL, fileName
            Else
                oClient.Delete info

                ' Remove UIDL from local uidl file.
                oUIDLManager.RemoveUIDL oServer, info.UIDL
            End If
        End If
    Next

    ' Quit
    oClient.Quit

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

ErrorHandle:

    MsgBox Err.Description
    If isUidlLoaded Then
        ' Update the uidl list to a text file and then we can load it next time.
        oUIDLManager.Update
    End If
End Sub

UIDLManager Object

With EAGetMail 4.0, it provides a new class named “UIDLManager”. This object provides an easy way to maintain UIDL between your server and your local client. How does it work? It stores UIDL collection to a local disk file and you can use this object to add, remove and search UIDL with this local file. Then you don’t have to handle UIDL in your code. Please click here to learn more detail.

Mark Email as Read on IMAP4/Exchange Server

With IMAP4/Exchange Web Service/WebDAV protocol, you can also mark the email as read on the server, but POP3 doesn’t support this feature. Please refer to MarkAsRead method to learn more detail.

[VB 6.0 Example - Retrieve Unread/New Email in IMAP4/EWS/WebDAV]

Because IMAP/EWS/WebDAV support read mail flag, with this feature, we can also retrieve unread/new email only from IMAP4/EWS/WebDAV like this

Option Explicit

Const MailServerPop3 = 0
Const MailServerImap4 = 1
Const MailServerEWS = 2
Const MailServerDAV = 3
Const MailServerMsGraph = 4

Const GetMailInfos_All = 1
Const GetMailInfos_NewOnly = 2
Const GetMailInfos_ReadOnly = 4
Const GetMailInfos_SeqRange = 8
Const GetMailInfos_UIDRange = 16
Const GetMailInfos_PR_ENTRYID = 32
Const GetMailInfos_DateRange = 64
Const GetMailInfos_OrderByDateTime = 128

Private Sub Command1_Click()
    Dim curpath As String
    Dim mailbox As String
    Dim oTools As New EAGetMailObjLib.Tools

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

    Dim oServer As New EAGetMailObjLib.MailServer
    oServer.Server = "imap.emailarchitect.net"
    oServer.User = "test@emailarchitect.net"
    oServer.Password = "testpassword"
    oServer.Protocol = MailServerImap4

    ' Enable SSL/TLS connection, most modern email servers require SSL/TLS by default
    oServer.SSLConnection = True
    oServer.Port = 993

    ' If your IMAP doesn't deploy SSL connection
    ' Please use
    ' oServer.SSLConnection = False
    ' oServer.Port = 143

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

    oClient.Connect oServer
    MsgBox "Connected"

    ' retrieve unread/new email only
    oClient.GetMailInfosParam.Reset
    oClient.GetMailInfosParam.GetMailInfosOptions = GetMailInfos_NewOnly

    Dim infos As EAGetMailObjLib.MailInfoCollection
    Set infos = oClient.GetMailInfoList()
    MsgBox infos.Count & " unread emails"

    Dim i As Long
    For i = 0 To infos.Count - 1
        Dim info As EAGetMailObjLib.MailInfo
        Set info = infos.Item(i)

        MsgBox "Index: " & info.Index & "; Size: " & info.Size & _
        "; UIDL: " & info.UIDL

        ' Receive email from IMAP4 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

         ' mark unread email as read, next time this email won't be retrieved again
        If Not info.Read Then
            oClient.MarkAsRead info, True
        End If

        ' if you don't want to leave a copy on server, please use
        ' oClient.Delete info
        ' instead of MarkAsRead
    Next

    ' Quit and expunge emails marked as deleted from IMAP4 server.
    oClient.Quit
    Exit Sub

ErrorHandle:
    MsgBox Err.Description
End Sub

Next Section

At next section I will introduce how to download email in background.

Appendix

Comments

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

See Also