Recall that one purpose of client.cf is
to make all messages appear to originate from the hub. The purpose
of a rule set
Hubset is to rewrite the sender's address
so that the mail message always appears to originate
from the hub machine.
From: user@client becomes From: user@hub
This could be done by rule set 3, but that would
affect all addresses, both recipient and sender, which is
not appropriate. Mail should not appear to be both to and
from the hub, but should appear
to be only from the hub.
It could also be done in rule set 1 (which we
will cover soon), but that
would affect all sender addresses. You don't want to rewrite
all sender addresses, just those that are being sent through the hub.
You may someday want to use
local delivery agents, and
the sender's address should be left unchanged for them.