I have been setup Redhat 9.0 with postfix 2.0 and squirrelmail 1.5.0

in all one computer.I have DNS on another computer ; mail server and DNS

work together yet .For configuration Postfix 2.0 is Standalone mailserver;

My mailserver already is work (can send and receive mail and work with

Outlook Express).

In webmail (squirrelmail 1.5.0) can receive mail

But I have some problems

when I send mail the message ERROR :

Transaction failed
Server replied:554 <someone@sample.net>:
Relay access denied


Please, help me . Should I fix in postfix or not ?