Sending of the message failed.  using port 587

I am using Mediacom ISP. I can receive emails but cannot send them. I used 2 different outgoing servers- smpt.mediacombb.net port 465 and port 587. I get 2 different error messages when I try to send. Sending of the message failed. using port 587 An error occurred while sending mail: Outgoing server (SMTP) error. The server responded: mcc-obgw-6001a.ext.cloudfilter.net cmsmtp ESMTP server temporarily not available AUP#DNS. Sending of the message failed. using port 465 The message could not be sent because connecting to Outgoing server (SMTP) smpt.mediacombb.net failed. The server may be unavailable or is refusing SMTP connections. Please verify that your Outgoing server (SMTP)correct and try again. Do either of these help to explain the problem?