Outlook OAuth2 SMTP is not authenticating with mailkit

Question

I'm currently working on one specific app that should send e-mail via outlook and using mailkit. App is logging in via oauth2 and imap authentication is OK, but not smtp.

I'm getting this exception:

535: 5.7.3 Authentication unsuccessful
[AM6P192CA0023.EURP192.PROD.OUTLOOK.COM]

Code sample

var publicClientApplication = PublicClientApplicationBuilder.Create(ClientId)
                .WithRedirectUri(RedirectUri)
                .Build();

var scopes = new string[]
{
    "email",
    "offline_access",
    "https://outlook.office.com/IMAP.AccessAsUser.All",
    "https://outlook.office.com/SMTP.Send"
};

var authToken = await publicClientApplication.AcquireTokenInteractive(scopes).ExecuteAsync();

SaslMechanism oauth2;

if (account.ImapClient.AuthenticationMechanisms.Contains("OAUTHBEARER"))
    oauth2 = new SaslMechanismOAuthBearer(authToken.Account.Username, authToken.AccessToken);
else
    oauth2 = new SaslMechanismOAuth2(authToken.Account.Username, authToken.AccessToken);

await SmtpClient.ConnectAsync(smtp.office365.com, 587, SecureSocketOptions.StartTls);
await SmtpClient.AuthenticateAsync(oauth2);

API permissions in app registration

API permissions

Any ideas?

Outlook OAuth2 SMTP is not authenticating with mailkit

0 Answers0