I did now also see an error in the plesk eventlog:
anyone seen that before?
System.Web.HttpException: Could not access 'CDO.Message' object. ---> System.Reflection.TargetInvocationException: Exception has been thrown by the target of an invocation. ---> System.Runtime.InteropServices.COMException (0x8004020E): The server rejected the sender address. The server response was: 501 Your domain does not seem to be valid. Could not find MX record for your domain.
--- 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 invokeAttr, Binder binder, Object target, Object[] args, ParameterModifier[] modifiers, CultureInfo culture, String[] namedParameters)
at System.Web.Mail.LateBoundAccessHelper.CallMethod(Object obj, String methodName, Object[] args)
--- End of inner exception stack trace ---
at System.Web.Mail.LateBoundAccessHelper.CallMethod(Object obj, String methodName, Object[] args)
at System.Web.Mail.CdoSysHelper.Send(MailMessage message)
at System.Web.Mail.SmtpMail.Send(MailMessage message)
at psabackup.CommonEnv.SendMail(String body, String from, String to, String subject, String eventSource)