Kolab-2 rejected messages

[Bradley M Alexander]

I needed to rebuild my mail server, for a number of reasons, including
the fact that it stopped accepting mail. Since it was running Kolab-1, I
looked at kolab-2, and it seemed to be maturing nicely (not to mention that
kolab-1 is getting a bit long in the tooth, with at least 2 known 
vulnerabilities against components).

So I built kolab2 with all patches through 8/17. Started the server, and
started configuring users. Checked my logs, and it appears that all inbound
messages are being rejected:

Sep 02 06:08:54 mekong <info> postfix/smtpd[10748]: NOQUEUE: reject: RCPT
from unknown[192.168.224.4]: 554 <logcheck at lakota>: Sender address rejected:
Invalid sender; from=<logcheck at lakota> to=<storm at tux.org>
proto=ESMTP helo=<lakota>]

Regardless of the sender, they are being rejected, whether from internal or
Internet email addresses.

What should I tweak to get this to accept emails?

Also, what is the right (kolab) way to make changes to the postfix main.cf?

Thanks,
--Brad