C#/ASP.NET/ASP MVC - Retrieve email using Google/Gmail OAuth 2.0 authentication + IMAP protocol

By default, you need to enable ” Allowing less secure apps” in Gmail, then you can retrieve email with user/password IMAP4 authentication.

However Google will disable traditional user authentication in the future, switching to Google OAuth is strongly recommended now.


Before you can use the following sample codes, you should download the EAGetMail Installer and install it on your machine at first. Full sample projects are included in this installer.

Install from NuGet

You can also install the run-time assembly by NuGet. Run the following command in the NuGet Package Manager Console:

Install-Package EAGetMail


If you install it by NuGet, no sample projects are installed, only .NET assembly is installed.

Add reference

To use EAGetMail POP3 & IMAP Component in your project, the first step is “Add reference of EAGetMail to your project”. Please create or open your project with Visual Studio, then go to menu -> Project -> Add Reference -> .NET -> Browse..., and select Installation path\Lib\[netversion]\EAGetMail.dll, click Open-> OK, the reference will be added to the project, you can start to use it to retrieve email and parse email in your project.

add reference in c#/vb.net/managed c++/cli

.NET assembly

Because EAGetMail has separate builds for .Net Framework, please refer to the following table and choose the correct dll.

Separate builds of run-time assembly for .Net Framework 2.0, 4.0, 4.5, 4.6.1, 4.7.2, 4.8.1, .NET 6.0, NET 7.0, .NET 8.0, .NET Standard 2.0 and .Net Compact Framework 2.0, 3.5.

File .NET Framework Version
Lib\net20\EAGetMail.dll Built with .NET Framework 2.0
It requires .NET Framework 2.0, 3.5 or later version.
Lib\net40\EAGetMail.dll Built with .NET Framework 4.0
It requires .NET Framework 4.0 or later version.
Lib\net45\EAGetMail.dll Built with .NET Framework 4.5
It requires .NET Framework 4.5 or later version.
Lib\net461\EAGetMail.dll Built with .NET Framework 4.6.1
It requires .NET Framework 4.6.1 or later version.
Lib\net472\EAGetMail.dll Built with .NET Framework 4.7.2
It requires .NET Framework 4.7.2 or later version.
Lib\net481\EAGetMail.dll Built with .NET Framework 4.8.1
It requires .NET Framework 4.8.1 or later version.
Lib\net6.0\EAGetMail.dll Built with .NET 6.0
It requires .NET 6.0 or later version.
Lib\net7.0\EAGetMail.dll Built with .NET 7.0
It requires .NET 7.0 or later version.
Lib\net8.0\EAGetMail.dll Built with .NET 8.0
It requires .NET 8.0 or later version.
Lib\netstandard2.0\EAGetMail.dll Built with .NET Standard 2.0
It requires .NET Standard 2.0 or later version.
Lib\net20-cf\EAGetMail.dll Built with .NET Compact Framework 2.0
It requires .NET Compact Framework 2.0, 3.5 or later version.
Lib\net35-cf\EAGetMail.dll Built with .NET Compact Framework 3.5
It requires .NET Compact Framework 3.5 or later version.

The Gmail IMAP and SMTP servers have been extended to support authorization via the industry-standard OAuth 2.0 protocol. Using OAUTH protocol, user can do authentication by Google Web Login instead of inputting user and password directly in application.

Create project in Google Developers Console

To retrieve email using Gmail OAuth in your application, you should create a project in Google Developers Console like this:

Create credentials (OAuth client id)

  • Click APIs & Services -> Dashboard -> Credentials

    google oauth Credentials
  • Click Credentials -> Create Credentials -> OAuth client ID -> Web application or Other (Desktop Application). It depends on your application type.

    google oauth Credentials
  • Input a name for your application, input your web applicaton url to receive authorization code at Authorized Redirect URIs. Desktop Application doesn’t require this step.

  • Click "Create", you will get client id and client secret

    google oauth client secret

Enable Gmail API

  • Enable Gmail API in "Library" -> Search "Gmail", then click "Gmail API" and enable it.

    enable Gmail API

Edit scopes

  • Set detail information for your project at "OAuth consent screen" -> "Edit App".

    edit Gmail oauth consent
  • Finally add "https://mail.google.com/" at "OAuth consent screen" -> "Edit App" -> "Scopes for Google API".

    enable Gmail scope

Authorized Redirect URIs

If you use OAuth in a web application, you should use a web page or controller to get authorization code from Google OAuth Server. So you need to add your page or web application routing path to Authorized Redirect URIs in APIs & Services -> Dashboard -> Credentials -> OAuth 2.0 Client IDs -> Your Client ID.

Authorized Redirect URIs

Enable TLS Strong Encryption Algorithms in .NET 2.0 and .NET 4.0

Because HttpWebRequest is used to get access token from web service. If you’re using legacy .NET framework (.NET 2.0 - .NET 3.5 and .NET 4.0 - 4.6.1), you need to enable Strong Encryption Algorithms to request access token:

Put the following content to a file named NetStrongEncrypt.reg, right-click this file -> Merge -> Yes. You can also download it from https://www.emailarchitect.net/webapp/download/NetStrongEncrypt.zip.

Windows Registry Editor Version 5.00





Use client id and client secret to request access token

You can use client id and client secret to get the user email address and access token like this:

  • Your application uses a web browser/browser control to open Oauth Url;
  • User inputs user and password in web authentication page, and then the Oauth server returns access token back to your application;
  • Your application uses access token to access resource on the server.
  • You can find full example codes in EAGetMail Installation Path\Samples_{Programming language/Developer Tool} project.

Access token expiration and refresh token

You don’t have to open browser to request access token every time. By default, access token expiration time is 3600 seconds, you can use the access token repeatedly before it is expired. After it is expired, you can use refresh token to refresh access token directly without opening browser. You can find full sample project in EAGetMail installation path to learn how to refresh token.


You should create your client id and client secret, do not use the client id from example codes in production environment, it is used for test purpose. If you got "This app isn't verified" information, please click "Advanced" -> Go to ... for test.

C# - Retrieve email using Google OAuth from Gmail IMAP server

Here is a console application which demonstrates how to use Google OAuth to do user authentication and retrieve email.


This sample cannot handle the event of Web Browser is closed by user manually before authentication is completed. You can refer to the better sample project which uses Web Browser Control in EAGetMail installation path.

using System;
using System.IO;
using System.Net;
using System.Net.Sockets;
using System.Text;
using System.Threading.Tasks;
using System.Runtime.InteropServices;
using EAGetMail;
using System.Globalization;

namespace EAGetMailCSharpKb
    class Program
        static void Main(string[] args)
            Console.WriteLine("  Sign in with Google                                             ");
            Console.WriteLine("   If you got \"This app isn't verified\" information in Web Browser, ");
            Console.WriteLine("   click \"Advanced\" -> Go to ... to continue test.");
            Console.WriteLine("Press any key to sign in...");

                Program p = new Program();
            catch (Exception ep)


        // 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")),

        void RetrieveMailWithXOAUTH2(string userEmail, string accessToken)
                // 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))

                MailServer oServer = new MailServer("imap.gmail.com",
                        accessToken, // use access token as password

                // Set IMAP OAUTH 2.0
                oServer.AuthType = ServerAuthType.AuthXOAUTH2;
                // Enable SSL/TLS connection, most modern email server require SSL/TLS by default
                oServer.SSLConnection = true;
                // Set IMAP4 SSL Port
                oServer.Port = 993;

                // Since EAGetMail 5.3.5, Gmail Rest API is supported as well. You can use the following code
                // to retrieve email using Gmail Rest API.
                // MailServer oServer = new MailServer("gmail.googleapis.com",
                //        userEmail,
                //        accessToken, // use access token as password
                //        ServerProtocol.GmailRestApi);

                // oServer.AuthType = ServerAuthType.AuthXOAUTH2;
                // oServer.SSLConnection = true;

                MailClient oClient = new MailClient("TryIt");
                // Get new email only, if you want to get all emails, please remove this line
                oClient.GetMailInfosParam.GetMailInfosOptions = GetMailInfosOptionType.NewOnly;

                Console.WriteLine("Connecting {0} ...", oServer.Server);

                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);

                    // Receive email from email 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 email as read to prevent retrieving this email again.
                    oClient.MarkAsRead(info, true);

                    // If you want to delete current email, please use Delete method instead of MarkAsRead
                    // oClient.Delete(info);

                // Quit and expunge emails marked as deleted from server.
            catch (Exception ep)

        // client configuration
        // You should create your client id and client secret,
        // do not use the following client id in production environment, it is used for test purpose only.
        const string clientID = "1072602369179-aru4rj97ateiho9rt4pf5i8l1r01mc16.apps.googleusercontent.com";
        const string clientSecret = "Lnw8r5FvfKFNS_CSEucbdIE-";
        const string scope = "openid%20profile%20email%20https://mail.google.com";
        const string authUri = "https://accounts.google.com/o/oauth2/v2/auth";
        const string tokenUri = "https://www.googleapis.com/oauth2/v4/token";

        static int GetRandomUnusedPort()
            var listener = new TcpListener(IPAddress.Loopback, 0);
            var port = ((IPEndPoint)listener.LocalEndpoint).Port;
            return port;

        async void DoOauthAndRetrieveEmail()
            // Creates a redirect URI using an available port on the loopback address.
            string redirectUri = string.Format("{0}/", GetRandomUnusedPort());
            Console.WriteLine("redirect URI: " + redirectUri);

            // Creates an HttpListener to listen for requests on that redirect URI.
            var http = new HttpListener();
            Console.WriteLine("Listening ...");

            // Creates the OAuth 2.0 authorization request.
            string authorizationRequest = string.Format("{0}?response_type=code&scope={1}&redirect_uri={2}&client_id={3}",

            // Opens request in the browser.

            // Waits for the OAuth authorization response.
            var context = await http.GetContextAsync();

            // Brings the Console to Focus.

            // Sends an HTTP response to the browser.
            var response = context.Response;
            string responseString = string.Format("<html><head></head><body>Please return to the app and close current window.</body></html>");
            var buffer = Encoding.UTF8.GetBytes(responseString);
            response.ContentLength64 = buffer.Length;
            var responseOutput = response.OutputStream;
            Task responseTask = responseOutput.WriteAsync(buffer, 0, buffer.Length).ContinueWith((task) =>
                Console.WriteLine("HTTP server stopped.");

            // Checks for errors.
            if (context.Request.QueryString.Get("error") != null)
                Console.WriteLine(string.Format("OAuth authorization error: {0}.", context.Request.QueryString.Get("error")));

            if (context.Request.QueryString.Get("code") == null)
                Console.WriteLine("Malformed authorization response. " + context.Request.QueryString);

            // extracts the code
            var code = context.Request.QueryString.Get("code");
            Console.WriteLine("Authorization code: " + code);

            string responseText = await RequestAccessToken(code, redirectUri);

            OAuthResponseParser parser = new OAuthResponseParser();

            var user = parser.EmailInIdToken;
            var accessToken = parser.AccessToken;

            Console.WriteLine("User: {0}", user);
            Console.WriteLine("AccessToken: {0}", accessToken);

            RetrieveMailWithXOAUTH2(user, accessToken);

        async Task<string> RequestAccessToken(string code, string redirectUri)
            Console.WriteLine("Exchanging code for tokens...");

            // builds the  request
            string tokenRequestBody = string.Format("code={0}&redirect_uri={1}&client_id={2}&client_secret={3}&grant_type=authorization_code",

            // sends the request
            HttpWebRequest tokenRequest = (HttpWebRequest)WebRequest.Create(tokenUri);
            tokenRequest.Method = "POST";
            tokenRequest.ContentType = "application/x-www-form-urlencoded";
            tokenRequest.Accept = "Accept=text/html,application/xhtml+xml,application/xml;q=0.9,*/*;q=0.8";

            byte[] _byteVersion = Encoding.ASCII.GetBytes(tokenRequestBody);
            tokenRequest.ContentLength = _byteVersion.Length;

            Stream stream = tokenRequest.GetRequestStream();
            await stream.WriteAsync(_byteVersion, 0, _byteVersion.Length);

                // gets the response
                WebResponse tokenResponse = await tokenRequest.GetResponseAsync();
                using (StreamReader reader = new StreamReader(tokenResponse.GetResponseStream()))
                    // reads response body
                    return await reader.ReadToEndAsync();

            catch (WebException ex)
                if (ex.Status == WebExceptionStatus.ProtocolError)
                    var response = ex.Response as HttpWebResponse;
                    if (response != null)
                        Console.WriteLine("HTTP: " + response.StatusCode);
                        using (StreamReader reader = new StreamReader(response.GetResponseStream()))
                            // reads response body
                            string responseText = await reader.ReadToEndAsync();

                throw ex;

        // Hack to bring the Console window to front.

        [DllImport("kernel32.dll", ExactSpelling = true)]
        public static extern IntPtr GetConsoleWindow();

        [return: MarshalAs(UnmanagedType.Bool)]
        public static extern bool SetForegroundWindow(IntPtr hWnd);

        public void BringConsoleToFront()

C# - Retrieve email using Google OAuth from Gmail IMAP server in ASP.NET/ASP MVC

If you use Google OAuth in ASP.NET/ASP MVC application, you should use a ASP.NET page or ASP MVC Controller to get authorization code instead of HttpListener. You need to add your ASP.NET page or ASP MVC Controller routing path to Authorized Redirect URIs in your Google project.

// Please add http://localhost:54098/oauth/token to Authorized redirect URIs in your Google/MS Azure project.
public ActionResult Token(string code)
    // code parameter is the authorization code returned by Google OAuth server,
    // then you can use it to request AccessToken
    // just like RequestAccessToken method in previous example

TLS 1.2 protocol

TLS is the successor of SSL, more and more SMTP servers require TLS 1.2 encryption now.

If your operating system is Windows XP/Vista/Windows 7/Windows 2003/2008/2008 R2/2012/2012 R2, you need to enable TLS 1.2 protocol in your operating system like this:

Enable TLS 1.2 on Windows XP/Vista/7/10/Windows 2008/2008 R2/2012



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