Mailing Application

I am not sure. If you are interested in suggestions then one possibility is to ping the server. That won't help if the server computer is up but the email server is not. I think you can send a noop to an email server to see if it responds.

You have not specified how you are sending the mail. Are you sending using SmtpClient? What is the SmtpClient.DeliveryMethod Property? Are you using try/catch? Are your receiving an SmtpException exception? Did you check the StatusCode property of the SmtpException exception?