Outbound Internet Emails with .msg attachments being converted to .txt

We're currently testing a data loss prevention application that is supposed to alert us when someone sends an outbound Internet email containing an Outlook message item as an attachment (.msg file).  Problem is that we're not being alerted.  We believe that Exchange is converting the .msg attachment to .txt.  When an Outlook user composes an email, attaches an Outlook message item (.msg) and sends it out to the Internet, our packet sniffer (Wireshark, Network Monitor, etc) is seeing the .msg attachment as .txt

My question: With Exchange outbound Internet email, is it behavior by design to convert .msg attachments to .txt ?  

This may explain why our data loss prevention application is not alerting us.  We run Exchange 2003 and Exchange 2010.  We've just starting looking into this and so far have experienced this situation with Outlook 2003/Exchange 2003.  Thanks.  
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bsohn417Asked:
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Carol ChisholmCommented:
Forefront for Exchange might do that.
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Carlisle_AgentCommented:
You can change the format of outgoing mail by tools/options/mail format. You have to be in HTML format in order for it to stay in .msg, which is by default. If you are already in HTML, I would call up the vendor and see if there is a hotfix for that.
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bsohn417Author Commented:
It turns out that neither Exchange nor the Ironport mail gateways are converting .MSG email attachments to plain text.  

We ran and reviewed packet captures to confirm the above. Several test messages were sent outbound Internet with .msg attachments.  

Below is a piece of the packet capture that contains any info related to the .MSG attachment.  The Content-Type and Content-class lines confirm that the .MSG format is being preserved.  The default content-type is actually plain/text, but here we see that it’s message/rfc822.

 
message/rfc822[RFC1521]

The message/rfc822 content type is used to enclose a complete message within a message. It is different from other MIME body parts in that it must be a fully formed RFC822 message, complete with headers.

 
http://msdn.microsoft.com/en-us/library/ms526229(v=exchg.10).aspx

 
------_=_NextPart_001_01CCCB2E.B7D3A7E7

Content-Type: message/rfc822

Content-Transfer-Encoding: 7bit

Content-class: urn:content-classes:message

MIME-Version: 1.0

Content-Type: multipart/alternative;

                boundary="----_=_NextPart_003_01CCCB2E.8C4B9700"

X-MimeOLE: Produced By Microsoft Exchange V6.5

Subject: DLP TEST

Date: Wed, 4 Jan 2012 17:16:46 -0500

X-MS-Has-Attach:

X-MS-TNEF-Correlator:

Thread-Topic: DLP TEST

Thread-Index: AczA7soAHDsq7cnCRJmXB+QvRtQu8g==

To: <johndoe@comcast.net>

 This is a multi-part message in MIME format.

------_=_NextPart_003_01CCCB2E.8C4B9700

 Several packet captures were run and the results were consistent and repeatable.

The .MSG format of the attachment is actually preserved all the way up to the recipient’s mail system.  I have confirmed this with an external Exchange system.  The recipient is able to open up the attachment in its intended form, i.e., .MSG.
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bsohn417Author Commented:
Issue resolved on own.
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