error 550

Pochemu ne otsylaetsja pochta s kompjutera vo vnutrennej seti nastroenogo maskaradingom na Linux... pishet sledujush'ee: "Delivery has failed on the enclosed message for the following reasons reported either by the mail delivery system on the mail relay host or by the local TCP/IP transport module: 550 <xxx@xxx.xxx>... Relaying denied" esli otsylat' pochtu s samogo servera to vsjo uhodit. Poluchaet pis'ma v oboih sluchajah. spasibo! :)