Announcing OAuth 2.0 Client Credentials Flow support for POP and IMAP protocols in Exchange Online

Nuget MailKit and Microsoft.Identity.Client. code tested.

using MailKit.Net.Pop3;
using MailKit.Security;
using Microsoft.Identity.Client;
using System;
using System.Collections.Generic;
using System.IO;
using System.Linq;
using System.Text;
using System.Threading.Tasks;

namespace MailKitTester
{
    class Program
    {
        public static string getMSOauth2Token(string clientId, string clientSecret, string tenantId)
        {
            
            string token;

            string authority = "https://login.microsoftonline.com/" + tenantId;
            const string scope = "https://outlook.office365.com/.default";

            IConfidentialClientApplication app;
            app = ConfidentialClientApplicationBuilder.Create(clientId)
                   .WithClientSecret(clientSecret)
                   .WithAuthority(authority)
                   .Build();

            string[] scopes = new string[]
            {
              scope,
              "offline_access"
            };
            token = app.AcquireTokenForClient(scopes).ExecuteAsync().Result.AccessToken;
            return token;

        }
        static void Main(string[] args)
        {
            string token = getMSOauth2Token("********", "********", "**********");

            using (var client = new Pop3Client())
            {
                client.Connect("Outlook.office365.com", 995, SecureSocketOptions.SslOnConnect);
                
                if (client.AuthenticationMechanisms.Contains("OAUTHBEARER") || client.AuthenticationMechanisms.Contains("XOAUTH2"))
                {
                    var oauth2 = new SaslMechanismOAuth2("email address removed for privacy reasons", token);
                    client.Authenticate(oauth2);
                }

                var msgCount = client.Count;
              
                client.Disconnect(true);
            }
        }
    }
}