Hi Chuha,
I've just realized that you and Craig are referring to the SendEmail Server Action.
That Action is not fully implemented yet.
At my company we only use the SendMimeEmail (as seen on the sample app), so i've never properly use the SendEmail action.
I'm a bit short on time right now, so i don't when i will be able to complete the attachment feature for that action.
Sorry for the misunderstanding.