Developing a Mail.app plug-in under OS X Lion: where to begin?

Question

I'm in the mood for developing a custom plug-in for Apple's default OS X mail client under OS X Lion (10.7). I can find a lot of plug-ins for older versions of Mail.app online, and some background information on the (officially unsupported and undocumented) plug-in architecture used by these old versions of Mail, but not for the newest version.

I know there are plug-ins for Lion's mail app so I know it's possible to do this, but I'm having a hard time finding out how to begin. Xcode offers templates for Address Book, Quartz Composer and Installer plug-ins, but not for Mail plug-ins.

I specifically do not want to work exclusively with AppleScripts because they won't allow me to do what I want to do: customize the application's interface, views and toolbars and such.

I am an experienced Objective-C developer and have built several apps for iOS, so the language and Xcode will pose no problems.

I think I just need to know 1) where/how to begin and 2) how to find reliable information about Mail.app's plug-in architecture. Can anybody point me in the direction of documentation, example projects or tutorials for developing such plug-ins? Of course, any other remarks, hints and tips are very welcome.

Thanks in advance!

Answer 1

There is at least one plugin for Mail.app which works on Lion. It's Growl Mail, plugin to connect Mail.app to Growl. Growl Mail has sources available on code.google, so, in my opinion, it's good point for start.

Oh, I almost forgot about second plugin, which I use, TruePreview. It has also sources available in internet.