Smtp exception could not send mails

System.Net.Mail.SmtpException: Failure sending mail. ---> System.Net.WebException: Unable to connect to the remote server ---> System.Net.Sockets.SocketException: No connection could be made because the target machine actively refused it xx.x.xx.xxx:25

my smtp host is above IP address i could not get mails it is w=throwing the above exception.