I have got the following Exception : System.Reflection.TargetInvocationException: Exception has been thrown by the target of an invocation. - System.Runtime.InteropServices.COMException (0x8004020F): The server rejected one or more recipient addresses. The server response was: 550 5.7.1 Unable to relay for ragaei[email protected] --- End of inner exception stack trace --- at System.RuntimeType.InvokeDispMethod(String name, BindingFlags invokeAttr, Object target, Object[] args, Boolean[] byrefModifiers, Int32 culture, String[] namedParameters) at System.RuntimeType.InvokeMember(String name, BindingFlags bindingFlags, Binder binder, Object target, Object[] providedArgs, ParameterModifier[] modifiers, CultureInfo culture, String[] namedParams) at System.Type.InvokeMember(String name, BindingFlags, invokeAttr, Binder binder, Object target, Object[] args, CultureInfo culture) at System.Web.Mail.SmtpMail.LateBoundAccessHelper.CallMethod(Type type, Object obj, String methodName, Object[] args) at System.Web.Mail.SmtpMail.LateBoundAccessHelper.CallMethod(Object obj, String methodName, Object[] args) public static void SendEmail(string _FromEmail, string _ToEmail, string _Subject, string _EmailBody) { // setup email header . SmtpMail.SmtpServer = "127.0.0.1"; MailMessage _MailMessage = new MailMessage(); _MailMessage.From = _FromEmail; _MailMessage.To = _ToEmail; _MailMessage.Subject = _Subject; _MailMessage.Body = _EmailBody; try { SmtpMail.Send(_MailMessage); } catch (Exception ex) { if (ex.InnerException != null) { String str = ex.InnerException.ToString(); } } }