Re:oh boy (Score 2, Informative)

It's not necessary to build a 3rd party mail client. As has been pointed out, you can use any mail client you like with Notes. The server supports: IMAP and POP as well as having a plug-in application for Outlook. So if your only complaint is about Notes as a mail client, there's no reason not to move onto a different client. Also, Notes has a full-featured webmail interface. That said, there is a group out there creating open-source apps for Notes: OpenNTF.org. They've created their own version of the mail template used by the Notes client. IBM has recently added some of their features back into the official mail client. Speaking of which, the mail template, and every other Notes template from IBM, is released along with the source code. I don't know of a Notes shop out there that hasn't made customizations to the default mail design.