[Remops] Postfix set up help

[Config]

I am completely new to using postfix and can't figure out what to do to 
fix my problem by reading the manual. I was trying to test my new 
remailer setup by sending the following subjects to it:

To root at inwtx.net
To remailer at mixmaster.inwtx.net

Subject: remailer-key
Subject: remailer-conf

Return error messages:

rcpt to: key at inwtx.net
550 5.1.1 key at inwtx.net: Recipient address rejected: User unknown in 
local recipient table

rcpt to: remailer-key at mixmaster.inwtx.net
554 5.7.1 remailer-key at mixmaster.inwtx.net: Relay access denied
rcpt to: remailer-conf at mixmaster.inwtx.net
554 5.7.1 remailer-conf at mixmaster.inwtx.net: Relay access denied

rcpt to: root at inwtx.net
250 2.1.5 Ok


My remailer.conf has everything going to mbox
MAILBOX /var/lib/mixmaster/mbox


As far as I can see, root at inwtx.net is the only test mail that made it 
through. Through deduction, it seems that I have to setup postfix to 
accept mixmaster.inwtx.net somewhere. Should this also be in the 
'mydestination =' line?
This is what is in it now:
mydestination = inwtx.net, localhost, localhost.localdomain, localhost
relayhost =


Secondly, it seems like I have to place any 'Recipient address' that 
comes in somewhere to keep them from rejecting (key in key at inwtx.net). 
Something about these files? local_recipient_maps, luser_relay, 
relay_domains

Can someone point me to the right files/parameters for this? The postfix 
manual has only served to confuse me.

Thanks.