Defining MIME types in IIS 6.0
MIME types or Multi-purpose Internet Mail Extensions extend the format of Internet mail to allow non-US-ASCII textual messages, non-textual messages, multipart message bodies, and non-US-ASCII information in message headers. To add new MIME types to IIS follow the steps below:

Ø       From the Internet Information Service Manager right click on (Local Computer) and select Properties

Ø       On the Properties page click on the MIME Types button

Ø       On the MME Types page click New

Ø       On the MIME Type page in the extension field enter the file extension to be added  ex: .ai

Ø       In the MIME Type field enter the description of the extension. For example .ai  description is application/postscript

Ø       Then click ok on the MIME Type and MIME Types pages

Note: The MIME description can either be provided by the customer requesting the addition or from a web search.