Exchange 2013 5.7.1 NDR

Exchange 2013 CU8
Windows Server 2012 R2 Standard

Here's the situation, an email is sent to a mailbox configured to forward to a MailContact with an external email address.  The email bounces when attempting to route to the external email address with a ‘5.7.1 Client does not have permission to send as this this sender' error.  I've managed Exchange 2010 in depth and configured forwarding to MailContacts many times without a problem.  Has something changed with 2013?
LVL 17
Jason CrawfordTransport NinjaAsked:
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Jason CrawfordTransport NinjaAuthor Commented:
I apologize for the delay in my reply, I have been out of the office for the last five days.  Those are interesting articles, and they do certainly highlight some of the changes to SMTP relaying with Exchange 2013.  I'm not 100% convinced this applies to my situation because these emails aren't being relayed, they're being forwarded to a MailContact with an external email address.  Here's the mail flow:

1. Email is sent to mailbox
2. The mailbox is configured to forward all email to
3. The email is then sent to the ExternalEmailAddress for

The setup above is not relaying (at least not my understanding of it).  Am I wrong?
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