I try to send a mail, relaying denied.

Sendmail
I change of proxy server to a CSM proxy in red hat linux version, when I try to send a mail it tell relaying denied. IP name loockup failed, and when someone send me a mail, they don’t arrive cause they send name@namedomain.co.cr here in Costa Rica but the sendmail needs to put the interface name like that = name@nameinterface.namedomain.co.cr, how can I configure it to receive like the first one