This example Xcode project shows how to send an email from within a Cocoa application. It does not require that the user have any mail client configured. It requires you to specify a mail server and account to use in the code.
This code was adapted from the Growl project. The original code can be found at: http://code.google.com/p/growl/source/browse/Plugins/Displays/MailMe/GrowlMailMeDisplay.m
It makes use of simple-mailer.py by Peter Hosey https://bitbucket.org/boredzo/simple-mailer/src/