sendmail?
 

i'd like to send a mail to this address (user@externaldomin.com)
this user is a local user (existing in /etc/passwd)
my domain is like "localname.localdomain"

i'd like that this mail will be sent locally to this user
i have add "externaldomain.com" as an alias of my host in /etc/hosts

when runnig sendmail -v user@externaldomain.com from this server;
it's nice
but when sending this mail from another machine in the lan; the mail is lost
(maybe relayed out of my lan)

plz what to do?

Have you setup your MX records correctly?