I don’t want let spammers take control of my mail server, I have configured my mail server but I am not sure how do I test my mail server for open relay? But what is an open mail realy?
An open mail relay occurs when a mail server processes a mail message where neither the sender nor the recipient is a local user. In this example, both the sender and the recipient are outside the local domain (or rather, the local IP range, for the technically inclined). The mail server is an entirely unrelated third party to this transaction. The message really has no business passing through this server.
I can check my server for open relay using any one of the following methods.
via Test mail server for an open relay.