Attachments appear as unknown.unk within Express

Within Express there are two potential reasons for the "unknown.unk" to occur

1. A Malformed message could be cause, below we will explain this further below.
2. Windows 2003 IIS 6 by default does not allow all extensions to be displayed or downloaded.

The below is an example of a malformed message header that can cause the "unknown.unk" to occur

------=_NextPart_000_0062_01C30346.2044F510
Content-Type: message/rfc822
Content-Transfer-Encoding: 7bit
Content-Disposition: attachment

The correct header should be:

------=_NextPart_000_0062_01C30346.2044F510
Content-Type: message/rfc822
Content-Transfer-Encoding: 7bit
Content-Disposition: attachment; filename="mydocument.doc"

As you can see within the header that will work there is an extra section ; filename="mydocument.doc". Express uses this value to show the attachment name. If it is not present then the attachments will be automatically be named as "unknown.unk". Email clients such as Outlook use a different method to retrieve the attachment name, therefore you will not see this issue.

This error in the header was present in messages coming from the service provider AOL. Since the creation of this KB document we believe that the service provider has addressed this issue in their email client.