> And if you wanted to modify your email client, or at least the one above (Mail.app, the default client for Mac), there is no clean way to extend it. There are

> And if you wanted to modify your email client, or at least the one above (Mail.app, the default client for Mac), there is no clean way to extend it. There are no plugins. There is no extension API. This is the result of many layers of cruft and bloat. I am going to say that it is probably a product decision in case of Mail.app. Whether Mail.app is a big steaming pile of cruft and bloat inside - nobody knows. Since it is closed source.