🚀 go-pugleaf

The local channel table specifies which addresses are local *to this host*.
So obviously  user@otherhost[.domain]  are not dealt with here, but rather
in the channel table which routes mail to the mail server (e.g. ether.chn).

Host hiding involves every machine being able to route mail for all users
in general domain via the aliases file.  You say it is impractical for you
to maintain such a list on every slave.  Well, there are two ways to avoid
this:
	(a) use yellow pages for the aliases
	(b) use nfs to enable sharing of /usr/lib/aliases*

Now let us assume that neither of these options of available to you;
maybe you have a hetrogeneous network with system V things etc.
In that case it sounds like you do not want host hiding using the multihost
feature.

Instead, you nominate your mail machine to treat "planet.bt.co.uk" as local
where you have the main aliases file. It can also have as its "official"
domain name "<machine>.planet.bt.co.uk" if mail machine is not called planet.

Slaves are given the domain name LHOST.planet.bt.co.uk.  In both cases do
not define multihost.  Instead specify that the domain name used on 
outgoing channel(s) is planet.bt.co.uk.  This is the key trick. In the
config file you give ldomain="planet.bt.co.uk" in the outgoing channel
specifications.

In the local channel table you specify LHOST.planet.bt.co.uk
and in ether (or whatever) channel table you specify
	planet.bt.co.uk		mail_machine

The effect is basically what you were after - all mail goes through
a central machine where the aliases database is kept - with the exception
of mail sent to "user" or "user@localhost".

-Jim.