thank you for the link.
However i've resolved the problem in another way.
My problem was that i wasn't able to save more than one infopath form with the same title, obviously, in sharepoint list.
So i created a rule that see if "title" on infopath form is the same "title" on sharepoint list. If it's the same it add a "Re:" string before the Title.
So if i've already saved a form named "hello" (that is i've sent an email with title=hello, because i use infopath to send email from sharepoint), the next infopath form that i open, if i write hello, it automatically call it "Re: hello" or something else if i want.