New File Extensions Blocked in Outlook 2003 SP3

Tuesday, February 12, 2008
After several months of testing, a client recently deployed Service Pack 3 for Microsoft Office 2003 to nearly 10,000 clients via WSUS. They have a scripted routine that they follow during testing of patches and updates to ensure that there are no interoperability issues, but of course, you can't test everything. I mean, how are you going to know that a certain update will prevent an HP 4200 printer from feeding from the secondary paper tray? And yes, I've actually seen that happen.

Well, shortly after deployment they start getting complaints that emails with links to Public Folders (XNK files) can't be opened on Outlook 2003. Could it be that Microsoft actually did this on purpose? After an hour or so of re-reading all the scattered documentation for Office SP3, including Information about certain file types that are blocked after you install Office 2003 Service Pack 3 and the Downloadable list of issues that the service pack fixes, I couldn't find anything that documented this change.

I opened a case with Microsoft and found that not only are XNK extenstions blocked, but several others are as well. Here's an unofficial list of the extensions blocked by Outlook 2003 SP3:

File ExtensionFile Type
.adeAccess Project Extension (Microsoft)
.adpAccess Project (Microsoft)
.appExecutable Application
.aspActive Server Page
.basBASIC Source Code
.batBatch Processing
.cerInternet Security Certificate File
.chmCompiled HTML Help
.cmdDOS CP/M Command File, Command File for Windows NT
.cplWindows Control Panel Extension (Microsoft)
.crtCertificate File
.cshcsh Script
.derDER Encoded X509 Certificate File
.exeExecutable File
.fxpFoxPro Compiled Source (Microsoft)
.gadgetWindows Vista gadget
.hlpWindows Help File
.htaHypertext Application
.infInformation or Setup File
.insIIS Internet Communications Settings (Microsoft)
.ispIIS Internet Service Provider Settings (Microsoft)
.itsInternet Document Set, Internet Translation
.jsJavaScript Source Code
.jseJScript Encoded Script File
.kshUNIX Shell Script
.lnkWindows Shortcut File
.madAccess Module Shortcut (Microsoft)
.mafAccess (Microsoft)
.magAccess Diagram Shortcut (Microsoft)
.mamAccess Macro Shortcut (Microsoft)
.maqAccess Query Shortcut (Microsoft)
.marAccess Report Shortcut (Microsoft)
.masAccess Stored Procedures (Microsoft)
.matAccess Table Shortcut (Microsoft)
.mauMedia Attachment Unit
.mavAccess View Shortcut (Microsoft)
.mawAccess Data Access Page (Microsoft)
.mdaAccess Add-in (Microsoft), MDA Access 2 Workgroup (Microsoft)
.mdbAccess Application (Microsoft), MDB Access Database (Microsoft)
.mdeAccess MDE Database File (Microsoft)
.mdtAccess Add-in Data (Microsoft)
.mdwAccess Workgroup Information (Microsoft)
.mdzAccess Wizard Template (Microsoft)
.mscMicrosoft Management Console Snap-in Control File (Microsoft)
.mshMicrosoft Shell
.msh1Microsoft Shell
.msh2Microsoft Shell
.mshxmlMicrosoft Shell
.msh1xmlMicrosoft Shell
.msh2xmlMicrosoft Shell
.msiWindows Installer File (Microsoft)
.mspWindows Installer Update
.mstWindows SDK Setup Transform Script
.opsOffice Profile Settings File
.pcdVisual Test (Microsoft)
.pifWindows Program Information File (Microsoft)
.plgDeveloper Studio Build Log
.prfWindows System File
.prgProgram File
.pstMS Exchange Address Book File, Outlook Personal Folder File (Microsoft)
.regRegistration Information/Key for W95/98, Registry Data File
.scfWindows Explorer Command
.scrWindows Screen Saver
.sctWindows Script Component, Foxpro Screen (Microsoft)
.shbWindows Shortcut into a Document
.shsShell Scrap Object File
.ps1Windows PowerShell
.ps1xmlWindows PowerShell
.ps2Windows PowerShell
.ps2xmlWindows PowerShell
.psc1Windows PowerShell
.psc2Windows PowerShell
.tmpTemporary File/Folder
.urlInternet Location
.vbVBScript File or Any VisualBasic Source
.vbeVBScript Encoded Script File
.vbsVBScript Script File, Visual Basic for Applications Script
.vsmacrosVisual Studio .NET Binary-based Macro Project (Microsoft)
.vswVisio Workspace File (Microsoft)
.wsWindows Script File
.wscWindows Script Component
.wsfWindows Script File
.wshWindows Script Host Settings File
.xnkExchange Public Folder Shortcut

Nothing p$%#es me off more than undocumented changes in functionality. At this point in time, this information is not documented ANYWHERE on Microsoft's website.

I certainly don't mind Microsoft fixing security holes, but for crying out loud, DOCUMENT IT!!! How do they expect us to roll out critical patches and updates if they change functionality and don't tell anyone? No one looks good when that happens.