Many system administrators do not want to be bothered with the
work needed to ensure that their system is able to reach all the
networks (and therefore systems) on all networks worldwide.
Instead of doing so, they would rather relay all outgoing mail
to another system that is known to be indeed ``smart''.
RELAY_HOST defines the UUCP hostname of such a smart neighboring
system. RELAY_MAILER defines the mailer used to relay the
messages there. It is important to note that setting these
parameters results in your outgoing mail being forwarded to this
remote system, which will affect the load of their system. Be
certain to get explicit agreement from the remote Postmaster
before you configure your system to use another system as a
general purpose relay host.