Ok.. it's 11:00PM here, so I'm going to bed, but here's some info that may help you. There is a content type called "message". It has a subtype of "rfc822". If you don't need to format it a specific way, but still need it parsed, try opening a filesystem object, read the file in, and write it to the client in a "message/rfc822" content type. I don't know if this will work, but I can play with it tomorrow.
Now, if you need to format it to the client's requirements, you'll probably need to parse the EML yourself. Meaning, create a filesystem object, read in line by line and put each line through a test checking for certain string criteria ("From:", "To:", etc). Then store the values in variables and display them where you want them to. The tricky part will be attachments. You'll need to create a separate ASP that just parses the EML, pulls the content type and name of the attachment and then sends just the data in that content type you pull. Then on your original page, you have a link to the attachment that points to your new ASP page, passing two parameters (the EML filename, and which attachment - if there are more than one). Clicking that link calls to the second ASP which parses the EML, pulls out the attachment and sends it to the client in the format the attachment is coded in.
It'd take some work, but it seems feasible.