Consider yourself a power user when it comes to email? Frustrated by your current email client? You're not alone. Although the Mac is home to numerous email clients - Mail, Entourage, Thunderbird, Eudora, Mailplane, Mailsmith, GyazMail, PowerMail, MailForge, Outspring Mail, and more - it's almost a given that a power user will have a set of desires that can't be met in a single program.
That may change, thanks to a grassroots project initiated by a blog post from NetNewsWire developer Brent Simmons. Within days, the Email Init mailing list that Simmons set up for discussion of just what such an email program would entail had received many hundreds of messages, and debate raged on topics ranging from whether or not the program should allow multiple instances of a single three-pane window to the best ways of handling conversation threading. An initial vision document written by Simmons lays out some of the decisions made in those early days; presumably subsequent discussions will generate revisions and refinements.
In the meantime, the likelihood of the project actually completing something increased with the election of John Gruber of Daring Fireball fame as president of the informal group. (Gruber has now taken over the group's Twitter account, if you want to follow in a low-bandwidth way.) Gus Mueller of Flying Meat Software (makers of Acorn and VoodooPad) will serve as the technical lead, but as an open source project, the assumption is that many people will contribute.
Having seen (and initiated) roughly similar projects in the past that never went anywhere, I'd say that Letters faces an uphill climb to meet the needs of the people who are the most fired-up about it now. Developing professional level software isn't easy, and although email often seems simple, it's an ecosystem that suffers from a vast number of edge cases, thanks to compliance problems among the many email servers and clients, and of course due to the massive abuse from spammers.
That said, much as I don't think shipping a sufficiently functional Letters 1.0 will be easy, I do think it's likely to happen, because enough of the people involved understand the challenges and have the necessary experience and skills to make it happen. It won't be quick though, since Gruber noted in a recent thread that Letters 1.0 may require Mac OS X 10.7, about which Apple has said nothing in public.
So if you have skills to contribute, or even just carefully considered opinions about how to improve upon the standard email experience, I encourage you to subscribe to the Email Init mailing list and see how you can help.