Server Rejects all incoming mail

The server is rejecting all incoming mail.... OS X Server SMTP Log states... NOQUEUE: reject: RCPT from 88-XX-XXX-XXX.dsl.zen.co.uk[88.XX-XXX-XXX]: 554 : Relay access denied; from= to= proto=ESMTP helo= tom has an account on OS X server 10.4.9 Chris is sending from another server.... Chris from outside mail server gets this response when sending to tom on the the OS X server... Received: 554 : Relay access denied