static void Main(string[] args) { UserCredential credential; using (var stream = new FileStream("credentials_dev.json", FileMode.Open, FileAccess.Read)) { string credPath = "token_Send.json"; credential = GoogleWebAuthorizationBroker.AuthorizeAsync( GoogleClientSecrets.Load(stream).Secrets, Scopes, "user", CancellationToken.None, new FileDataStore(credPath, true)).Result; Console.WriteLine("Credential file saved to: " + credPath); } // Create Gmail API service. var service = new GmailService(new BaseClientService.Initializer() { HttpClientInitializer = credential, ApplicationName = ApplicationName, }); // Define parameters of request. string plainText = "To:[email protected]\r\n" + "Subject: Gmail Send API Test\r\n" + "Content-Type: text/html; charset=us-ascii\r\n\r\n" + "<h1>TestGmail API Testing for sending <h1>"; var newMsg = new Google.Apis.Gmail.v1.Data.Message(); newMsg.Raw = SendMail.Base64UrlEncode(plainText.ToString()); service.Users.Messages.Send(newMsg, "me").Execute(); Console.Read(); }