App request: OmniMail. There are lots of third party email applications for OS X and iOS, but nothing has yet been enough for me to move away from Apple’s own. I think Omni could do it. Plus integrating some OmniFocus functionality could be amazing.
You might want to really check out MailMate. Amazing mail app. And nicely integrated with OmniFocus: a simple keyboard shortcut auto-magically sends an email off to OF with needed details (task name, due date, etc.). Plus MailMate natively works with Markdown, is quick, search function is to-die-for, and many other pro features.
It doesn’t look that pretty, but it functions amazingly well.