I was not sure if opening this issue, since Mailer component is experimental and 4.3 version is still in beta. Anyway, may is about to end and it looks like an important feature is missing in Mailer. I'm not even sure if this is a bug or a new feature (I opted for last one, being a new component)

My expectation is to replace current combo of Swiftmailer library and Swifmailer bundle with new combo of Mailer and MIME components, and to get more or less the same functionalities.
So, for example, I expect to see some info in the profiler and in the web debug toolbar (you know, the old good envelope icon linked to info about headers, text, rendered message, etc.).

I couldn't find anything in current mailer, for example the NullTransport is doing absolutely nothing