It would probably be the same as how would do it in K2.net 2003.  You would configure a specific mail account to send the new request to via email.  On the backend, you need to create a email listener program/service that polls the designated mailbox.  The second portion would be to parse the email message body and translate the body data into an actual StartProcessInstance call.

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if you use MOSS/WSS you can use the incoming mail feature (http://technet.microsoft.com/en-us/library/cc263260.aspx) that's allow you to add an item in a document library when an email is received to a specific account. Then, in a K2 part, you can create a Sharepoint Event Process that catch the "item created" event in this document library.

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