I'm willing to kick in $200 for a lightweight mail client that does the following:

IMAP4/s

Runs in the background, polls the mail server at intervals for new mail and notifies of new messages. The polling application can actually run entirely in the background and seperate from the main application and launch the actual mail app only when you wish to view or respond to messages.

SMPTS

You might want to include dropbear support for ssh tunneling in the case that imap4s and smtps aren't reasonable.

Extra credit for e-mail address integration with the built-in contacts.

You can base your code on this:

http://www.pi-sync.net/html/projects.html