Which MIME types of mails are most popular?

I have to add into my server app an ability to receive a mail via POP3 and process it. The processing is: to convert it correctly into plain text (WCHAR* string).So I am looking for a ready component that would will do the conversion. I want the component to support as much MIME types as possible. There are lot of them – see http://www.iana.org/assignments/media-types/index.html.

The question is: which MIME types can I meet with most probability – except the well-known text/plain and text/html? The clients I expect will be mostly Outlook и Outlook Express; but others are possible too.