When using Exchange Server 2010 and Exchange Server 2003 in co-existence, where your mailbox is on an Exchange Server 2010 mailbox server, you send an e-mail with an attachment to a user with a mailbox on Exchange Server 2003.
When the Exchange Server 2003 recipient views the message using OWA for Exchange Server 2003, they see a paperclip icon denoting an attachment on the message. However, when the message is opened no attachment can be viewed. When using Microsoft Office Outlook, the recipient sees the attachment correctly.
This behavior is by design and is the result of enabling Silverlight on the Exchange Server 2010 Client Accss Server (CAS).
Log onto the CAS server with the appropriate Administrator permissions.
Disable silverlight from the Exchange Server 2010 Management Shell using the following cmdlet.
Set-OwaVirtualDirectory -Identity "Servername\Owa (Default Web Site)" -SilverLightEnabled $False
Where Servername is the name of the Client Access Server. This action must be performed on each Client Access Server in the organization that is used.
Note When an Outlook Web App mailbox policy is applied to a mailbox, it will override the settings of the virtual directory.
Use a client that does not use the Silverlight (e.g., where Silverlight is not installed) to compose the e-mail message.
All impacted e-mail messages have the Content-ID field in the message. Messages that are not impacted do not. WebDAV sees the attachments as inline, if this property is set. You can view the Properties of the message to determine if Content-ID is present.
Adding the Content-Id is by design in the Silverlight scenario. This change was introduced in Exchange Server 2010 Service Pack 1.
We have also noted that this problem can occur on handheld devices that use a CDO/MAPI or EWS connection to Exchange. The solution also resolves the issue for those devices.