How to implement OAUTH 2.0 in Outlook using Ultimate Mail

Hi I'm trying to authenticate use OAUTH2 token based authentication for Outlook but not able to get authenticated. Whenever Authenticate is called using a token [**Authenticate(string Token, ImapAuthenticationMethod ImapAuthenticationMethod.OAuth2)**] it throws the following error ComponentPro.Net.Mail.ImapException: **AUTHENTICATE failed (NO).** at ComponentPro.Net.Mail.Imap.c_47d8efdd(String , ImapResponse , Boolean ) at ComponentPro.Net.Mail.Imap.c_56b07853(String ) at ComponentPro.Net.Mail.Imap.c_5e2380a4(String , String , ImapAuthenticationMethod , c_e ) at ComponentPro.Net.Mail.Imap.c_c224912a(String , String , ImapAuthenticationMethod ) at ComponentPro.Net.Mail.Imap.Authenticate(String token, ImapAuthenticationMethod method) I'm using the following code: try { var _task = Task.Run(() => { return GetAccessToken(); }); _task.Wait(); var tokenResult = _task.Result; AccessToken = tokenResult.AccessToken; MailClient = new Imap(); MailClient.Config = new ImapConfig() { AllowedTlsVersions = TlsSslVersion.TLS12 }; MailClient.Connect("outlook.office365.com", 993, SslSecurityMode.Implicit); string initAuthInfo = GenerateSASLToken(); MailClient.Authenticate(initAuthInfo, ImapAuthenticationMethod.OAuth20); if (MailClient.IsAuthenticated) ReadMailbox(); else throw new Exception($"User authentication failed."); } catch (Exception ex) { throw ex } finally { if (MailClient.IsConnected) MailClient.Disconnect(); } private async Task GetAccessToken() { try { var confidentialClientApplication = ConfidentialClientApplicationBuilder .Create(ClientId) .WithClientSecret(ClientSecret) .WithTenantId(TenantId) .Build(); var scopes = new string[] { "https://outlook.office365.com/.default" }; return await confidentialClientApplication.AcquireTokenForClient(scopes).ExecuteAsync(); } catch (Exception ex) { throw; } } private string GenerateSASLToken() { string authData = string.Format("user={0}{1}auth=Bearer {2}{1}{1}", UserName, '\x1', AccessToken); return Convert.ToBase64String(Encoding.ASCII.GetBytes(authData)); } If I use the same credential (SASL token) and call the **SendCommand** the response received is **OK AUTHENTICATE completed.** MailClient.SendCommand("AUTHENTICATE", new object[2] { "XOAUTH2", initAuthInfo }); ImapResponse _response = MailClient.ReadResponse(); Regards

Hi Your error suggests a scope issue . Check below post [NO AUTHENTICATE failed][1] This can solved by using correct scope suggested by Microsoft For Microsoft, we recommend https://outlook.office.com/IMAP.AccessAsUser.All or https://outlook.office.com/POP.AccessAsUser.All, and offline_access. Thank you for contacting us [1]: https://confluence.atlassian.com/jirakb/imap-setup-fails-with-authenticate-failed-error-in-logs-in-jira-server-185401609.html