There are a number of reasons why this might be the case.
- See http://knicksmith.blogspot.com/2007/03/exchange-2007-and-outlook-2003-where.html. An issue was resolved by Microsoft in Exchange 2003 Service Pack 1 where Exchange 2007 was incorrectly causing Outlook 2003 to hide inline attachments. Even though you could not see the attachment, if you flagged the email, or clicked forward on the email, the attachment would appear correctly. Also if you selected Save attachments from the file menu, it would still save the attachments. OWA is not affected by this.
- See http://social.technet.microsoft.com/Forums/en-US/exchangesvrclients/thread/478c326b-486b-461c-9141-dd544b245c75. Symptoms: You can see the attachment in OWA but not in any of the current versions of Outlook. Outlook blocks the attachment completely and there is no way to retrieve it through this interface. This is also more likely to happen when an inhouse application has been programmed to send email with attachments. if the MIME is formatted incorrectly then Outlook will not display it. RFC 2387 describes the intended use of multipart/related:
http://www.ietf.org/rfc/rfc2387.txt:
"The Multipart/Related media type is intended for compound objects consisting of several inter-related body parts. For a Multipart/Related object, proper display cannot be achieved by individually displaying the constituent body parts."
Steps to resolve this issue involve changing the MIME header to Multipart/Mixed instead of Multipart/Related. Multipart/Related will cause the attachment to be considered inline by Outlook. As there is no reference to the attachment in the body, it will then effectively be ignored. OWA has more smarts and is able to determine if an attachment is really inline or not. If it finds no reference to the attachment in the body of the email then it displays the attachment as a separate entity.
