smtp authentication

[David Southwell]

Hi

 I am really ignorant about this issue.

I am running postfix on freebsd 7.0 using a dynamic IP address and am getting 
requests to turn on smtp authentication for outgoing mails to reach servers 
such as yahoo.com but do not know how to do it.

I am using kmail as a client.

If anyone could point me in the right direction I would be most grateful.

Thank you

David