use domain from setting à sending credentials against smtp server

src/Yavsc.Server/Settings/SmtpSettings.cs

@@ -7,6 +7,7 @@ namespace  Yavsc
         public int Port { get; set; }
         public string UserName { get; set; }
         public string Password { get; set; }
+        public string Domain { get; set; }
 
         public bool EnableSSL { get; set; }
     }

src/Yavsc/Services/MailSender.cs

@@ -65,7 +65,7 @@ namespace Yavsc.Services
                         SecureSocketOptions.Auto);
                     if (smtpSettings.UserName!=null) {
                         NetworkCredential creds = new NetworkCredential(
-	                    smtpSettings.UserName, smtpSettings.Password, smtpSettings.Host);
+	                    smtpSettings.UserName, smtpSettings.Password, smtpSettings.Domain);
                         await sc.AuthenticateAsync(System.Text.Encoding.UTF8, creds, System.Threading.CancellationToken.None);
                       }