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Using UIDL Function to Mark the Email has been downloaded/read in Visual C++

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 Visual C++.

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 Visual C++ 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.

[Visual C++ 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.

#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;
    const int MailServerMsGraph = 4;

    // 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);

    try
    {
        IMailServerPtr oServer = NULL;
        oServer.CreateInstance(__uuidof(EAGetMailObjLib::MailServer));

        oServer->Server = _T("imap.emailarchitect.net");
        oServer->User = _T("test@emailarchitect.net");
        oServer->Password = _T("testpassword");
        oServer->Protocol = MailServerImap4;

        // Enable SSL Connection, most modern email servers require SSL/TLS by default
        oServer->SSLConnection = VARIANT_TRUE;
        oServer->Port = 993;

        // If your IMAP doesn't deploy SSL connection
        // Please use
        // oServer->SSLConnection = VARIANT_FALSE;
        // oServer->Port = 143;

        IMailClientPtr oClient = NULL;
        oClient.CreateInstance(__uuidof(EAGetMailObjLib::MailClient));
        oClient->LicenseCode = _T("TryIt");

        oClient->Connect(oServer);
        _tprintf(_T("Connected\r\n"));

        IMailInfoCollectionPtr infos = oClient->GetMailInfoList();
        _tprintf(_T("Total %d emails\r\n"), infos->Count);

        IToolsPtr oTools = NULL;
        oTools.CreateInstance(__uuidof(EAGetMailObjLib::Tools));

        for (long i = 0; i < infos->Count; i++)
        {
            IMailInfoPtr pInfo = infos->GetItem(i);

            TCHAR szFile[MAX_PATH+1];
            memset(szFile, 0, sizeof(szFile));

            // Using IMAP4 UIDL as file name
            ::wsprintf(szFile, _T("%s\\%s.eml"),
                szMailBox, (const TCHAR*)pInfo->UIDL);

            if(oTools->ExistFile(szFile) == VARIANT_TRUE)
            {
                // this email has been download, we don't need to retrieve it again.
                continue;
            }

            // Receive email from IMAP4 server
            IMailPtr oMail = oClient->GetMail(pInfo);

            // Save email to local disk
            oMail->SaveAs(szFile, VARIANT_TRUE);

            // Do not delete email
        }

        // Delete method just mark the email as deleted,
        // Quit method expunge the emails from server exactly.
        oClient->Quit();
    }
    catch (_com_error &ep)
    {
        _tprintf(_T("Error: %s"), (const TCHAR*)ep.Description());
    }

    return 0;
}

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.

#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;
    const int MailServerMsGraph = 4;

    // 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;
}

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.

[Visual C++ 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

#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;
    const int MailServerMsGraph = 4;

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

    // 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);

    try
    {
        IMailServerPtr oServer = NULL;
        oServer.CreateInstance(__uuidof(EAGetMailObjLib::MailServer));

        oServer->Server = _T("imap.emailarchitect.net");
        oServer->User = _T("test@emailarchitect.net");
        oServer->Password = _T("testpassword");
        oServer->Protocol = MailServerImap4;

        // Enable SSL Connection,  most modern email servers require SSL/TLS by default
        oServer->SSLConnection = VARIANT_TRUE;
        // Set 993 SSL IMAP4 port
        oServer->Port = 993;

        // If your IMAP doesn't deploy SSL connection
        // Please use
        // oServer->SSLConnection = VARIANT_FALSE;
        // oServer->Port = 143;

        IMailClientPtr oClient = NULL;
        oClient.CreateInstance(__uuidof(EAGetMailObjLib::MailClient));
        oClient->LicenseCode = _T("TryIt");

        oClient->Connect(oServer);
        _tprintf(_T("Connected\r\n"));

        // retrieve unread/new email only
        oClient->GetMailInfosParam->Reset();
        oClient->GetMailInfosParam->GetMailInfosOptions = GetMailInfos_NewOnly;

        IMailInfoCollectionPtr infos = oClient->GetMailInfoList();
        _tprintf(_T("Total %d unread emails\r\n"), infos->Count);

        for (long i = 0; i < infos->Count; i++)
        {
            IMailInfoPtr pInfo = infos->GetItem(i);

            // Generate a random file name by current local datetime,
            // You can use your method to generate the filename if you do not like it
            TCHAR szFile[MAX_PATH + 1];
            SYSTEMTIME curtm;
            ::GetLocalTime(&curtm);
            ::wsprintf(szFile, _T("%s\\%04d%02d%02d%02d%02d%02d%03d%d.eml"),
                szMailBox,
                curtm.wYear,
                curtm.wMonth,
                curtm.wDay,
                curtm.wHour,
                curtm.wMinute,
                curtm.wSecond,
                curtm.wMilliseconds,
                i);

            // Receive email from POP3 server
            IMailPtr oMail = oClient->GetMail(pInfo);

            // Save email to local disk
            oMail->SaveAs(szFile, VARIANT_TRUE);

            // mark unread email as read, next time this email won't be retrieved again
            if( pInfo->Read == VARIANT_FALSE)
            {
                oClient->MarkAsRead(pInfo, VARIANT_TRUE);
            }

            // if you don't want to leave a copy on server, please use
            // oClient->Delete(pInfo);
            // instead of MarkAsRead
        }

        // Delete method just mark the email as deleted,
        // Quit method expunge the emails from server exactly.
        oClient->Quit();
    }
    catch (_com_error &ep)
    {
        _tprintf(_T("Error: %s"), (const TCHAR*)ep.Description());
    }

    return 0;
}

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