550 5.7.1 Unable to relay from *any* Exchange Server account

Greetings, folks...just this week I've stumbled into this problem at our office, and after reading all the variations (and trying more than a few of them), I remain baffled.  So much so that I signed up for this service!

Here's the detail and I'll try to point out where it differs from the others:

SBS 2003 Standard (with Exchange 2003, sp1 -- tried updating to SP2 today in anticipation of this post, but unable to uninstall the Internet Message Filter thingy -- don't know if that's related or not)

All our users can receive e-mail from the internet, and to/from each other, but cannot send out.  They get NDRs that look like this:

> Your message
>
>  To:      ******@swbell.net
>  Subject: test 1126
>  Sent:    Thu, 5 Jun 2008 11:27:01 -0500
>
> did not reach the following recipient(s):
>
> *******@swbell.net on Thu, 5 Jun 2008 11:27:02 -0500
>    You do not have permission to send to this recipient.  For
> assistance, contact your system administrator.
>    <orthopedicresources.com #5.7.1>
>
> Reporting-MTA: dns; TIGER.orthores.local
>
> Final-Recipient: RFC822; ******@swbell.net
> Action: failed
> Status: 5.7.1
> X-Supplementary-Info: <orthopedicresources.com #5.7.1>
> X-Display-Name: ******@swbell.net

I can telnet to the SMTP server both from internal and external networks, and get a similar message from the SMTP server:

> 250 2.1.0 ******@orthopedicresources.com....Sender OK
> rcpt to:******@swbell.net
> 550 5.7.1 Unable to relay for ******@swbell.net

During my first pass at solving this yesterday, I somehow managed to break the ability of our Exchange Server to send out the NDRs above...reinstallling Exchange this morning solved that one.

As I said, I have done the dreaded reinstall of Exchange (not the first step of course), made sure that the authenticated users have the ability to relay, made sure the IP addresses on the LAN are allowed.

This is a problem both for Outlook client users and OWA users, btw.

Note the reporting MTA above is using our internal .local name -- could that be our problem, and how do I change this?

Thanks in advance, gurus!
--
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