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

[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.

using System;
using System.Globalization;
using System.IO;
using EAGetMail; //add EAGetMail namespace

namespace receiveemail
{
    class Program
    {
        static void Main(string[] args)
        {
            try
            {
                // Create a folder named "inbox" under current directory
                // to save the email retrieved.
                string localInbox = string.Format("{0}\\inbox", Directory.GetCurrentDirectory());
                // If the folder is not existed, create it.
                if (!Directory.Exists(localInbox))
                {
                    Directory.CreateDirectory(localInbox);
                }

                MailServer oServer = new MailServer("imap.emailarchitect.net",
                            "test@emailarchitect.net",
                            "testpassword",
                            ServerProtocol.Imap4);

                // Enable SSL/TLS connection, most modern email server require SSL/TLS by default
                oServer.SSLConnection = true;
                oServer.Port = 993;

                // if your server doesn't support SSL/TLS, please use the following codes
                // oServer.SSLConnection = false;
                // oServer.Port = 143;

                MailClient oClient = new MailClient("TryIt");
                oClient.Connect(oServer);

                MailInfo[] infos = oClient.GetMailInfos();
                Console.WriteLine("Total {0} email(s)\r\n", infos.Length);
                for (int i = 0; i < infos.Length; i++)
                {
                    MailInfo info = infos[i];
                    Console.WriteLine("Index: {0}; Size: {1}; UIDL: {2}",
                        info.Index, info.Size, info.UIDL);

                    // Using IMAP UIDL as the file name.
                    string fileName = String.Format("{0}.eml", info.UIDL);
                    string fullPath = string.Format("{0}\\{1}", localInbox, fileName);

                    if(File.Exists(fullPath))
                    {
                    // This email has been downloaded before, do not download it again.
                        continue;
                    }

                    // Receive email from IMAP4 server
                    Mail oMail = oClient.GetMail(info);

                    Console.WriteLine("From: {0}", oMail.From.ToString());
                    Console.WriteLine("Subject: {0}\r\n", oMail.Subject);

                    // Save email to local disk
                    oMail.SaveAs(fullPath, true);

                    // Do not delete email from IMAP4 server.
                }

                // Quit and expunge emails marked as deleted from IMAP4 server.
                oClient.Quit();
                Console.WriteLine("Completed!");
            }
            catch (Exception ep)
            {
                Console.WriteLine(ep.Message);
            }
        }
    }
}

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 POP3/IMAP4/Exchange Web Service/WebDAV protocols.

using System;
using System.Globalization;
using System.IO;
using EAGetMail; //add EAGetMail namespace

namespace receiveemail
{
    class Program
    {
        // Generate an unqiue email file name based on date time
        static string _generateFileName(int sequence)
        {
            DateTime currentDateTime = DateTime.Now;
            return string.Format("{0}-{1:000}-{2:000}.eml",
                currentDateTime.ToString("yyyyMMddHHmmss", new CultureInfo("en-US")),
                currentDateTime.Millisecond,
                sequence);
        }

        static void Main(string[] args)
        {
            bool isUidlLoaded = false;
            bool isLeaveCopy = true; // leave a copy of message on server.

             // UIDL is the identifier of every email on POP3/IMAP4/Exchange 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.
            // UIDLManager wraps the function to write/read uidl record from a text file.
            UIDLManager oUIDLManager = new UIDLManager();

            try
            {
                // Create a folder named "inbox" under current directory
                // to save the email retrieved.
                string localInbox = string.Format("{0}\\inbox", Directory.GetCurrentDirectory());
                string uidlFile = string.Format("{0}\\uidl.txt", localInbox);

                // If the folder is not existed, create it.
                if (!Directory.Exists(localInbox))
                {
                    Directory.CreateDirectory(localInbox);
                }

                 // Load existed uidl records to UIDLManager
                oUIDLManager.Load(uidlFile);
                isUidlLoaded = true;

                MailServer oServer = new MailServer("pop3.emailarchitect.net",
                        "test@emailarchitect.net",
                        "testpassword",
                        ServerProtocol.Pop3);

                // Enable SSL/TLS connection, most modern email server require SSL/TLS by default
                oServer.SSLConnection = true;
                oServer.Port = 995;

                // if your server doesn't support SSL/TLS, please use the following codes
                // oServer.SSLConnection = false;
                // oServer.Port = 110;

                MailClient oClient = new MailClient("TryIt");
                oClient.Connect(oServer);

                MailInfo[] infos = oClient.GetMailInfos();
                Console.WriteLine("Total {0} email(s)\r\n", infos.Length);

                // Remove the local uidl that is not existed on the server,
                oUIDLManager.SyncUIDL(oServer, infos);
                oUIDLManager.Update();

                for (int i = 0; i < infos.Length; i++)
                {
                    MailInfo info = infos[i];
                    if (oUIDLManager.FindUIDL(oServer, info.UIDL) != null)
                    {
                        // This email has been downloaded before
                        continue;
                    }

                    Console.WriteLine("Retrieving {0}/{1}...", i + 1, infos.Length);

                    Mail oMail = oClient.GetMail(info);

                    Console.WriteLine("From: {0}", oMail.From.ToString());
                    Console.WriteLine("Subject: {0}\r\n", oMail.Subject);

                    // Generate an unqiue email file name based on date time.
                    string fileName = _generateFileName(i + 1);
                    string fullPath = string.Format("{0}\\{1}", localInbox, fileName);

                    // Save email to local disk
                    oMail.SaveAs(fullPath, true);

                    if (isLeaveCopy)
                    {
                        // Add uidl to uidl file to avoid we retrieve it next time.
                        oUIDLManager.AddUIDL(oServer, info.UIDL, fileName);
                    }
                    else
                    {
                        Console.WriteLine("Deleting ...");
                        oClient.Delete(info);

                        // Remove UIDL from local uidl file.
                        oUIDLManager.RemoveUIDL(oServer, info.UIDL);
                    }
                }

                // Quit and expunge emails marked as deleted from POP3 server.
                oClient.Quit();
                Console.WriteLine("Completed!");
            }
            catch (Exception ep)
            {
                Console.WriteLine(ep.Message);
            }

            // Update the uidl list to local uidl file and then we can load it next time.
            if (isUidlLoaded)
            {
                oUIDLManager.Update();
            }
        }
    }
}

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.

[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

using System;
using System.Globalization;
using System.IO;
using EAGetMail; //add EAGetMail namespace

namespace receiveemail
{
    class Program
    {
        // Generate an unqiue email file name based on date time
        static string _generateFileName(int sequence)
        {
            DateTime currentDateTime = DateTime.Now;
            return string.Format("{0}-{1:000}-{2:000}.eml",
                currentDateTime.ToString("yyyyMMddHHmmss", new CultureInfo("en-US")),
                currentDateTime.Millisecond,
                sequence);
        }

        static void Main(string[] args)
        {
            try
            {
                // Create a folder named "inbox" under current directory
                // to save the email retrieved.
                string localInbox = string.Format("{0}\\inbox", Directory.GetCurrentDirectory());
                // If the folder is not existed, create it.
                if (!Directory.Exists(localInbox))
                {
                    Directory.CreateDirectory(localInbox);
                }

                MailServer oServer = new MailServer("imap.emailarchitect.net",
                        "test@emailarchitect.net",
                        "testpassword",
                        ServerProtocol.Imap4);

                // Enable SSL/TLS connection, most modern email server require SSL/TLS by default
                oServer.SSLConnection = true;
                oServer.Port = 993;

                // if your server doesn't support SSL/TLS, please use the following codes
                // oServer.SSLConnection = false;
                // oServer.Port = 143;

                MailClient oClient = new MailClient("TryIt");
                oClient.Connect(oServer);

                // retrieve unread/new email only
                oClient.GetMailInfosParam.Reset();
                oClient.GetMailInfosParam.GetMailInfosOptions = GetMailInfosOptionType.NewOnly;

                MailInfo[] infos = oClient.GetMailInfos();
                Console.WriteLine("Total {0} unread email(s)\r\n", infos.Length);
                for (int i = 0; i < infos.Length; i++)
                {
                    MailInfo info = infos[i];
                    Console.WriteLine("Index: {0}; Size: {1}; UIDL: {2}",
                        info.Index, info.Size, info.UIDL);

                    // Receive email from IMAP4 server
                    Mail oMail = oClient.GetMail(info);

                    Console.WriteLine("From: {0}", oMail.From.ToString());
                    Console.WriteLine("Subject: {0}\r\n", oMail.Subject);

                    // Generate an unqiue email file name based on date time.
                    string fileName = _generateFileName(i + 1);
                    string fullPath = string.Format("{0}\\{1}", localInbox, fileName);

                    // Save email to local disk
                    oMail.SaveAs(fullPath, true);

                    // mark unread email as read, next time this email won't be retrieved again
                    if(!info.Read)
                    {
                        oClient.MarkAsRead(info, true);
                    }

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

                // Quit and expunge emails marked as deleted from IMAP4 server.
                oClient.Quit();
                Console.WriteLine("Completed!");
            }
            catch (Exception ep)
            {
                Console.WriteLine(ep.Message);
            }
        }
    }
}

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