External e-mail attachments always seen as inline attachments with Exchange 2010

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Our Office Add-in is using MAPI flags to define whether e-mail attachments are inline or not. Currently we have problems with the customers that work with Exchange 2010, and then only for the external e-mail messages .

In the Exchange 2010 - Office 2010 environment all attachments in external emails looks like inline attachments. This conclusion is based on the fact that MAPI properties PR_ATTACHMENT_HIDDEN=True and both PR_ATTACH_CONTENT_ID and PR_ATTACH_CONTENT_LOCATION are set.

When the same e-mail message is send to the Exchange 2003 - Office 2010 environment then all attachments are seen as “real” attachments


Please note that " Save All Attachments" works fine in both of these environments.

Following is a part of Internet Header from one of the external e-mails with attachments:

" X-MimeOLE: Produced By Microsoft Exchange V6.5

Content-Class: urn:content-classes:message

MIME-Version: 1.0

Content-Type: multipart/related; type=" multipart/alternative" ;
boundary=" ----_=_NextPart_001_01CB9D25.F1B2D1B6"

X-MS-Has-Attach: yes


Do you know what can cause such a behavior?

Novak Wu

First, I would like to confirm the following questions:

1. What"s the message format the sender is used to send the problematic message?

2. What"s the message format of delivered problematic message on the receiver"s side?

3. Does the issue occur on each Outlook 2010 client in your Exchange system?

At this stage, I suggest you refer to the following steps to troubleshoot the issue.

1. Please click “Attach File” in Outlook when trying to send an email and check whether the attachment displays inline.

2. Please change the message format as HTML instead of RTF on both sender and receiver"s sides, and then try to reproduce the issue again

Also, I would like to share you the following article to troubleshoot the issue.






Thanks Novak.

Hereby answers on your questions:
1. Sender message format is HTML
2. HTML is message format on Receiver side as well
3. The problem occurs on every Outlook 2010 client for the particular customer (Exchange 2010 with Office 2010)
1.In Outlook message attachment is shown as a real attachment both on the sender and receiver side
2.As mentioned above, both sender and receiver part already have message in HTML format.
I might use the wrong wording - by inline I thought embedded.
The reason that our Addin consider attachment in the problematic email as embedded attachment is that for our Addin (based on the msdn documentation) we build the logic that when attachment is embedded in the HTML message then it is stored as regular attachment, but it has extra property (PR_ATTACH_CONTENT_ID or PR_ATTACH_CONTENT_LOCATION) set.

Problematic email messages show attachments as a real attachments when open in Outlook but the MIME flags values I get using Outlook PropertyAccessor show that both PR_ATTACH_CONTENT_ID and PR_ATTACH_CONTENT_LOCATION are set -> our Add-in will consider this attachment as embedded.

In the MSDN article you are referring to it is not clear where/how I can change the order of body parts.

P.S. I am on vacation next week so my colleague, Nenad, will take over contact about this issue for a week.
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