I'm new to Linux, and I've read up a bit on PostFix, but I'm not having much luck getting this working:

I've implemented Linux (FC5) box running Postfix 2.3.4 as a dedicated outbound relay for an Exchange 2003 server. The Exchange server sits in a subdomain, "exch.example.com" and sends email out from that domain.

In this Relaying role, can Postfix perform a Masquerade operation on outbound email from the Exchange server that drops the subdomain portion of the address from "@exch.example.com" to "@example.com"?

Seems that I might be doing something wrong. The email relays fine, but the subdomain portion of the address is not removed.

No mailboxes reside on the Postfix box. It is strictly a relay.

Should I use canonical methods instead?

Thanks in advance for your assistance.

Update:

Looks like it works on part of the message header, but not the part that seems to matter. These look good:

X-eSCM-MailFrom: <jdoe@example.com>
.
.
.
Return-Path: jdoe@example.com

But PostFix doesn't change this one, and it appears to take precedence:
From: "John Doe" <jdoe@exchange.example.com>
X-MimeOLE: Produced By Microsoft Exchange V6.5

Can that address be changed via PostFix on a relay server? Any insight is greatly appreciated.