Thanks for proposing your help but I ll translate myself, and I already have someone to correct me.
My zimlet doesn't save in eml format. You can easily use REST to save a single mail .eml in a zip file.
Use a url like this :
http://server.domain.com/user/~/?id=502&fmt=zip (502 is the id of the mail).
My zimlet save the body of the mail with some information like date and expeditor and save it in a .txt file, without the attachments of course.