UIDLManager.Load Method


Loads UIDL to current UIDLManager instance from local UIDL file.

[Visual Basic 6.0]
Public Sub Load( FileName As String _
)
[Visual C++]
public: Load(BSTR FileName
);

Parameters

FileName
The UIDL full file path to load.

Remarks

Sometimes the developers want to leave a copy of email on the POP3/IMAP4/Exchange server for backup, so they don't delete the email after the email was received. The common issue is how to detect if the email has been retrieved by the application already, otherwise, all the emails on the server will be retrieved again and again. In this case, we should use the Unique Identifier (UIDL) to avoid to receive the same email more than once.

Using Unique Identifier (UIDL)

The mail server assigns an unique identifier for every email in the same account. You can get the UIDL for every email by MailInfo.UIDL property. To avoid to receive the same email twice, the best way is storing the UIDL of email retrieved to a text file or database. Next time before you retrieve the email, compare your local uidl list with remote uidl. If this uidl exists in your local uidl list, then you don't receive it, otherwise you should receive it.

Difference with UIDL in POP3/IMAP4/Exchange Web Service/WebDAV

UIDL is always unique in IMAP4 and it is always increasing integer. UIDL in POP3 can be any valid asc-ii characters, and the UIDL may be reused by POP3 server if the email with the UIDL has been deleted from the server, so we suggest that you should remove the uidl from your local uidl list if the uidl is no longer existed on the POP3 server. UIDL is also unique in Exchange Web Service/WebDAV, but the UIDL is string but not integer. 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. 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. For Exchange Web Service/WebDAV, although the UIDL is always unique in your email account, but UIDL may also contain invalid characters for file name.

Total Solution

UIDLManager 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.

UIDL File Format

With UIDLManager, you can use any file name as the UIDL local file, but we suggest that you use different UIDL file for different email account. In the UIDL file, each line presents a UIDL information.

"mailserver#user#protocol","UIDL","Local File Name","Download Date Time","Flags"
"mailserver#user#protocol","UIDL1","Local File Name1","Download Date Time","Flags"
        

You can use UIDLManager to record the UIDL of the email that you have downloaded; you can also associate the local file name and flags to UIDLItem object. Then you can use UIDLManager to detect if the email has been downloaded, when it has been downloaded. If it has been downloaded, what local file it has saved to.

Example

[[Visual Basic 6.0, VBScript, Visual C++, Delphi] The following example demonstrates how To retrieve email with EAGetMail POP3 & IMAP Component, but it doesn't demonstrates the events and mail parsing usage. To get the full samples of EAGetMail, please refer to Samples section.

[Visual Basic 6.0]
Const MailServerPop3 = 0
Const MailServerImap4 = 1
Const MailServerEWS = 2
Const MailServerDAV = 3

Public Sub ReceiveMail( _
ByVal sServer As String, _
ByVal sUserName As String, _
ByVal sPassword As String, _
ByVal bSSLConnection As Boolean, _
ByVal bLeaveCopy)
    
    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"

    Dim oTools As New EAGetMailObjLib.Tools 
    oTools.CreateFolder localInbox

    Dim oServer As New EAGetMailObjLib.MailServer
    oServer.Server = sServer
    oServer.User = sUserName
    oServer.Password = sPassword
    oServer.Protocol = MailServerPop3
    oServer.SSLConnection = bSSLConnection
    
    If oServer.SSLConnection Then
        oServer.Port = 995
    Else
            oServer.Port = 110
    End If

On Error GoTo ErrorHandle:

    ' 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.
    ' 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 mailInfos As EAGetMailObjLib.MailInfoCollection
    Set mailInfos = oClient.GetMailInfoList()

    MsgBox mailInfos.Count & " emails"

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

    Dim i As Long
    For i = 0 To mailInfos.Count - 1

        Dim oInfo As EAGetMailObjLib.MailInfo
        Set oInfo = mailInfos.Item(i)

        MsgBox "Index: " & i + 1 & "; Size: " & oInfo.Size & _
        "; UIDL: " & oInfo.UIDL

        Dim oUIDLItem As UIDLItem
        Set oUIDLItem = oUIDLManager.FindUIDL(oServer, oInfo.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 + 1) & ".eml"

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

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


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

                ' Remove UIDL from local uidl file.
                oUIDLManager.RemoveUIDL oServer, oInfo.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


[VBScript] Const MailServerPop3 = 0 Const MailServerImap4 = 1 Const MailServerEWS = 2 Const MailServerDAV = 3 Public Sub ReceiveMail( _ ByVal sServer , _ ByVal sUserName, _ ByVal sPassword, _ ByVal bSSLConnection, _ ByVal bLeaveCopy) Dim localInbox Dim isUidlLoaded isUidlLoaded = False ' Create a folder named "inbox" ' to save the email retrieved. localInbox = "d:\inbox" Dim oTools Set oTools = CreateObject("EAGetMailObj.Tools") oTools.CreateFolder localInbox Dim oServer Set oServer = CreateObject("EAGetMailObj.MailServer") oServer.Server = sServer oServer.User = sUserName oServer.Password = sPassword oServer.Protocol = MailServerPop3 oServer.SSLConnection = bSSLConnection If oServer.SSLConnection Then oServer.Port = 995 Else oServer.Port = 110 End If ' 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. ' 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 Set oUIDLManager = CreateObject("EAGetMailObj.UIDLManager") oUIDLManager.Load localInbox & "\uidl.txt" isUidlLoaded = True Dim oClient Set oClient = CreateObject("EAGetMailObj.MailClient") oClient.LicenseCode = "TryIt" oClient.Connect oServer WScript.Echo "Connected" Dim mailInfos Set mailInfos = oClient.GetMailInfoList() WScript.Echo mailInfos.Count & " emails" ' Remove the local uidl that is not existed on the server, oUIDLManager.SyncUIDLEX oServer, mailInfos ' Update result back to uidl file oUIDLManager.Update Dim i For i = 0 To mailInfos.Count - 1 Dim oInfo Set oInfo = mailInfos.Item(i) WScript.Echo "Index: " & i + 1 & "; Size: " & oInfo.Size & _ "; UIDL: " & oInfo.UIDL Dim oUIDLItem Set oUIDLItem = oUIDLManager.FindUIDL(oServer, oInfo.UIDL) ' If this email has not been retrieved before, then get it If oUIDLItem Is Nothing Then Dim fileName fileName = oTools.GenFileName(i + 1) & ".eml" Dim fullFileName fullFileName = localInbox & "\" & fileName Dim oMail Set oMail = oClient.GetMail(oInfo) oMail.SaveAs fullFileName, True If bLeaveCopy Then ' Add the email uidl to uidl file to avoid we retrieve it next time. oUIDLManager.AddUIDL oServer, oInfo.UIDL, fileName Else oClient.Delete oInfo ' Remove UIDL from local uidl file. oUIDLManager.RemoveUIDL oServer, oInfo.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 End Sub
[Visual C++] #include "stdafx.h" #include <windows.h> #include "eagetmailobj.tlh" using namespace EAGetMailObjLib; DWORD _getCurrentPath(LPTSTR lpPath, DWORD nSize) { DWORD dwSize = ::GetModuleFileName(NULL, lpPath, nSize); if (dwSize == 0 || dwSize == nSize) { return 0; } // Change file name to current full path LPCTSTR psz = _tcsrchr(lpPath, _T('\\')); if (psz != NULL) { lpPath[psz - lpPath] = _T('\0'); return _tcslen(lpPath); } return 0; } int _tmain(int argc, _TCHAR* argv[]) { const int MailServerPop3 = 0; const int MailServerImap4 = 1; const int MailServerEWS = 2; const int MailServerDAV = 3; // Initialize COM environment ::CoInitialize(NULL); /// Create a folder named "inbox" under current exe file directory // to save the emails retrieved. TCHAR szPath[MAX_PATH + 1]; _getCurrentPath(szPath, MAX_PATH); TCHAR szMailBox[MAX_PATH + 1]; wsprintf(szMailBox, _T("%s\\inbox"), szPath); // Create a folder to store emails ::CreateDirectory(szMailBox, NULL); IUIDLManagerPtr uidlManager; bool isUidlLoaded = false; // leave a copy of message on server bool leaveCopy = true; try { IMailServerPtr oServer = NULL; oServer.CreateInstance(__uuidof(EAGetMailObjLib::MailServer)); oServer->Server = _T("pop3.emailarchitect.net"); oServer->User = _T("test@emailarchitect.net"); oServer->Password = _T("testpassword"); oServer->Protocol = MailServerPop3; // Enable SSL/TLS connection, most modern email servers require SSL/TLS by default oServer->SSLConnection = VARIANT_TRUE; oServer->Port = 995; // If your POP3 doesn't deploy SSL connection // Please use // oServer->SSLConnection = VARIANT_FALSE; // oServer->Port = 110; IMailClientPtr oClient = NULL; oClient.CreateInstance(__uuidof(EAGetMailObjLib::MailClient)); oClient->LicenseCode = _T("TryIt"); // 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. TCHAR szUidlFile[MAX_PATH + 1]; wsprintf(szUidlFile, _T("%s\\uidl.txt"), szMailBox); uidlManager.CreateInstance(__uuidof(EAGetMailObjLib::UIDLManager)); uidlManager->Load(szUidlFile); isUidlLoaded = true; oClient->Connect(oServer); _tprintf(_T("Connected\r\n")); IMailInfoCollectionPtr infos = oClient->GetMailInfoList(); _tprintf(_T("Total %d emails\r\n"), infos->Count); // Remove the local uidl that is not existed on the server, uidlManager->SyncUIDLEX(oServer, infos); uidlManager->Update(); for (long i = 0; i < infos->Count; i++) { IMailInfoPtr pInfo = infos->GetItem(i); IUIDLItemPtr uidl = uidlManager->FindUIDL(oServer, pInfo->UIDL); if (uidl != nullptr) { // This email has been downloaded before continue; } // Generate an unique file named based on current date time // If you don't like it, you can use your method to generate file name TCHAR szFile[MAX_PATH + 1]; SYSTEMTIME curtm; ::GetLocalTime(&curtm); wsprintf(szFile, _T("%04d%02d%02d%02d%02d%02d%03d%d.eml"), curtm.wYear, curtm.wMonth, curtm.wDay, curtm.wHour, curtm.wMinute, curtm.wSecond, curtm.wMilliseconds, i); TCHAR szFullPath[MAX_PATH + 1]; wsprintf(szFullPath, _T("%s\\%s"), szMailBox, szFile); IMailPtr oMail = oClient->GetMail(pInfo); oMail->SaveAs(szFullPath, VARIANT_TRUE); if(leaveCopy) { // Add the email uidl to uidl file to avoid we retrieve it next time. uidlManager->AddUIDL(oServer, pInfo->UIDL, szFile); } else { oClient->Delete(pInfo); // Remove UIDL from local uidl file. uidlManager->RemoveUIDL(oServer, pInfo->UIDL); } } } catch(_com_error &ep) { _tprintf(_T("Error: %s"), (const TCHAR*)ep.Description()); } //update the uidl list to a text file and then we can load it next time. if (uidlManager != nullptr && isUidlLoaded) { uidlManager->Update(); } return 0; }
[Delphi] unit Unit1; interface uses Windows, Messages, SysUtils, Variants, Classes, Graphics, Controls, Forms, Dialogs, StdCtrls, StrUtils, EAGetMailObjLib_TLB; // Add EAGetMail unit type TForm1 = class(TForm) Button1: TButton; procedure Button1Click(Sender: TObject); private { Private declarations } public { Public declarations } end; const MailServerPop3 = 0; MailServerImap4 = 1; MailServerEWS = 2; MailServerDAV = 3; var Form1: TForm1; implementation {$R *.dfm} procedure TForm1.Button1Click(Sender: TObject); var oServer: TMailServer; oClient: TMailClient; oTools: TTools; oMail: IMail; oUIDLManager: TUIDLManager; infos: IMailInfoCollection; oInfo: IMailInfo; localInbox, fileName, fullFileName: WideString; isUidlLoaded: Boolean; leaveCopy: Boolean; i: integer; begin // set current thread code page to system default code page. SetThreadLocale(GetSystemDefaultLCID()); // leave a copy of message on server leaveCopy := true; isUidlLoaded := false; // 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. oUIDLManager := TUIDLManager.Create(Application); try oTools := TTools.Create(Application); localInbox := GetCurrentDir() + '\inbox'; oTools.CreateFolder(localInbox); oUIDLManager.Load(localInbox + '\uidl.txt'); isUidlLoaded := true; oServer := TMailServer.Create(Application); oServer.Server := 'pop3.emailarchitect.net'; oServer.User := 'test@emailarchitect.net'; oServer.Password := 'testpassword'; oServer.Protocol := MailServerPop3; // Enable SSL/TLS Connection, most modern email server require SSL/TLS connection by default. oServer.SSLConnection := true; // Set 995 SSL POP3 port oServer.Port := 995; // If your POP3 server doesn't deploy SSL connection // Please use // oServer.SSLConnection := false; // oServer.Port := 110; oClient := TMailClient.Create(Application); oClient.LicenseCode := 'TryIt'; oClient.Connect1(oServer.DefaultInterface); ShowMessage('Connected!'); infos := oClient.GetMailInfoList(); ShowMessage(Format('Total %d email(s)', [infos.Count])); // Remove the local uidl that is not existed on the server, oUIDLManager.SyncUIDLEX(oServer.DefaultInterface, infos); oUIDLManager.Update(); for i := 0 to infos.Count - 1 do begin oInfo := infos.Item[i]; // This email has not been retrieved before, then get it if oUIDLManager.FindUIDL(oServer.DefaultInterface, oInfo.UIDL) <> nil then continue; // this email has been downloaded, do not receive it again // 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 := oTools.GenFileName(i) + '.eml'; fullFileName := localInbox + '\' + fileName; // Receive email from email server oMail := oClient.GetMail(oInfo); ShowMessage('From: ' + oMail.From.Address + #13#10 + 'Subject: ' + oMail.Subject); // Save email to local disk oMail.SaveAs(fullFileName, true); if leaveCopy Then begin // Add the email uidl to uidl file to avoid we retrieve it next time. oUIDLManager.AddUIDL(oServer.DefaultInterface, oInfo.UIDL, fileName); end else begin oClient.Delete(oInfo); // Remove UIDL from local uidl file. oUIDLManager.RemoveUIDL(oServer.DefaultInterface, oInfo.UIDL); end; end; // Quit and expunge emails marked as deleted from email server oClient.Quit; except on ep:Exception do ShowMessage('Error: ' + ep.Message); end; // Update the uidl list to a text file and then we can load it next time. if isUidlLoaded then oUIDLManager.Update(); end; end.

See Also

MailInfo.UIDL Property

Online Tutorials

Using UIDL Function to Mark the Email has been downloaded/read in VB6 - Tutorial
Using UIDL Function to Mark the Email has been downloaded/read in Delphi - Tutorial
Using UIDL Function to Mark the Email has been downloaded/read VC++ - Tutorial