Well as it turns out IIS 6 does not serve up unknown MIME Types on purpose for security reasons.
http://support.microsoft.com/kb/326965

Creating MIME Types for a Web site or directory (IIS 6.0)
http://www.microsoft.com/technet/pr...ad27-4800-adfb-13c4ae39a602.mspx?pf=true

MIME Types in IIS 4/5
http://www.microsoft.com/technet/pr.../iis/maintain/featusability/mimeiis.mspx

David Wang: HOWTO: Allow file downloads (including .exe) on IIS 6.0
http://blogs.msdn.com/david.wang/archive/2005/07/11/Allow_file_downloads_on_IIS_6.aspx

David Wang: HOWTO: Allow file downloads (including .exe) on IIS 6.0, Part 2
http://blogs.msdn.com/david.wang/ar...loads-including-exe-on-IIS-6-Part-2.aspx

David wang: HOWTO: IIS 6 Request Processing Basics, Part 1
http://blogs.msdn.com/david.wang/ar..._6_Request_Processing_Basics_Part_1.aspx

David Wang: Why Wildcard application mapping can disable Default Document resolution
http://blogs.msdn.com/david.wang/ar...disable_Default_Document_resolution.aspx

David Wang: Thoughts on IIS Security vs Apache
http://blogs.msdn.com/david.wang/archive/2005/09/30/Thoughts_on_IIS_Security_vs_Apache.aspx

David Wang: Thoughts on IIS Security vs Apache, Part 2
http://blogs.msdn.com/david.wang/archive/2005/10/01/Thoughts-on-IIS-Security-vs-Apache-Part-2.aspx


I've made the required changes and now my attachment folder allows some of the other file types to be downloaded.


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