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Hello, i have an app that send emails correctly, the problem is later that day a error shows up saying "Authentication Error code:334". I think that i need to refresh the token or maybe gmail smtp have a limit for free emails.

What I have tried:

I tried to find on internet but i only find code for web apps, and mine is desktop

Here's my code

                using (var stream = new FileStream("credential.json", FileMode.Open, FileAccess.Read))
                    string credPath = "token.json";
                    credential = GoogleWebAuthorizationBroker.AuthorizeAsync(
                        Scopes = new[] { "" },
                        new FileDataStore(credPath, true)).Result;
                    Console.WriteLine("Credential file saved to: " + credPath);
                var service = new GmailService(new BaseClientService.Initializer()
                    HttpClientInitializer = credential,
                    ApplicationName = ApplicationName,
                var message = new MimeKit.MimeMessage();
                message.From.Add(new MimeKit.MailboxAddress("User", ""));
                message.To.Add(new MimeKit.MailboxAddress("Test", ""));
                message.Subject = "Test";
                message.Body = new MimeKit.TextPart("plain")
                    Text = "Test"
                using (var client = new MailKit.Net.Smtp.SmtpClient())
                    client.Connect("", 587);
                    // use the access token 
                    var oauth2 = new MailKit.Security.SaslMechanismOAuth2(credential.UserId, credential.Token.AccessToken);
            catch (Exception e)

1 solution

Pretty sure you asked the same thing recently .. this post Q: How do I authenticate with an OAUTH2 access token? · Issue #606 · jstedfast/MailKit · GitHub[^]

points out that
await credential.RefreshTokenAsync(CancellationToken.None);
seems to be the missing piece - have a read anyway and see if anything there helps you.
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