Reza:
Your question begins to lead into a discussion of laws and ethics. You should use one of your own servers to route the email. You could, but should not, route your mail through an external server (If they have proper security setup you will be unable to do so, for example Yahoo and Hotmail). If you do find an external server which will allow you to route the mail then you should notify the administrator of that server. I am not sure what the exact laws are on the subject and if it is even legal to route through an external server.

The exact answer to your question, I do not know what the server name is for Yahoo or Hotmail...and I am pretty sure you will be unable to route email through there.

Typically the server name would be the email address. For example, RezaKia@yahoo.com... the server name would be: mail.yahoo.com.

HTH

Wes