Does Mail.app support plugins (API)?

Question

Does Mail.app (Mac) have an API where developers can create plugins for Mail?

I'm confused by an official Knowledge Base article Apple wrote that states:

Apple does not support the installation or use of third-party plugins with Mail.app. Third-party Mail plugins are located in ~/Library/Mail/Bundles and /Library/Mail/Bundles.

So plugin's are located in /Bundles, but they are not supported?

I'm confused.

Answer 1

"Not supported" just means literally: "We don´t care if it breaks anything, so continue at your own risk - we won´t fix or support it". There are Bundles around, and I think the best overview you can find if on the "Hawk Wings" Website.

Indeed, Apple doesn´t offer a public API, it keeps it private. This blog entry tries to explain in quite some detail how to work with that private API nevertheless, and maybe could provide a good starting point for you.