sendmail kak mail hub?

Vsem dobroe vremya sutok! Kak ya ponimayu pochtoviy hub eto: 1. Zapis klassa A v dns naprimer hub.domain.net 2. MX zapisi naprimer pismo.domain.net ukazivayushie na A zapis 3. V virtusertable ya ukazivayu chto pisma prihodashie na @pismo.domain.net perenapravlat na %1@mail.domain.ru 4. V access.db upominayu chto pisma prihodashiye na mail.domain.ru prinimat i perenapravlyat. delayu makemap nujnim faylam, perezapuskayu sendmail. pri popitke otpravleniya soobsheniye na user@pismo.domain.net sendmail rugaetsa tak: MX list for pismo.domain.net points back to hub.domain.net To chto ya pravelno nastroul perenapravleniye dokazivaet to chto u menya na mashine akaunta user net a na tom servake na kotoriy ya perenapravlayu yest, i kogda pisheh na user@pismo.domain.net prihodit otvet ob akaunte user s mail.domain.ru toest recipient user@pismo.domain.net ok podskjite pliz pochemu rugaetsa sendmail?