Without the Premium account you can just create a „Custom Action“ an choose „open url“ and put this in
agenda://x-callback-url/create-note?project-title=Inbox&title=%5Bmessage_subject%5D%20(email)&text=From%3A%20%5Bmessage_sender_name%5D%20%3C%5Bmessage_sender%5D%3E%0ATo%3A%20%5Bmessage_to%5D%0A___%0A%5Bmessage_simplified_body%5D%0A___%0A%5Bmessage_linkback%5D%0A%23email&on-the-agenda=true&date=today
I have a project called „Inbox“, but one can change the name of the project-title at the beginning of the x-callback-url. I think with Apple‘s workflow-app it must be possible to create a workflow where you can choose the project and maybe add attachments.