When you install Microsoft Office 2003 Service Pack 3 (SP3), and then you try to use Microsoft Office Outlook 2003 to open an attachment that has one of the file name extensions that are listed in the "Cause" section, the attachment does not open.
This behavior occurs because the following file name extensions have been added to the blocked file types in Office 2003 SP3.
Level 1 file types added as blocked by Outlook 2003 SP3
DER Encoded X509 Certificate File
Windows Vista Gadget
Developer Studio Build Log
Exchange Public Folder Shortcut
These files may contain executable code that could potentially harm your computer. Therefore, these attachments have been blocked in Outlook 2003 SP3.
For information about the file types that are restricted or disabled in Outlook 2003, visit the following Microsoft Web site: