relay in sendmail

>promiscuous_relay
>                By default, the sendmail configuration files do not permit
>                mail relaying (that is, accepting mail from outside your
>                domain and sending it to another host outside your domain).
>                This option sets your site to allow mail relaying from any
>                site to any site.  In general, it is better to control the
>                relaying more carefully with the access db and the 'R'
>                class ($=R).  Domains can be added to class 'R' by the
>                macros RELAY_DOMAIN or RELAY_DOMAIN_FILE (analogously to
>                MASQUERADE_DOMAIN and MASQUERADE_DOMAIN_FILE, see below).