Unfortunately this is not possible currently but you can customize the notification email in /components/com_easydiscuss/themes/simplistic/emails/email.subscription.site.new.html.php

how mark, what is the string that i have to change?

I have no idea what you want to remove / add but if you want to just remove the contents of the email, you should remove the $postContent from the email template.

I want to remove the text of the reply (see the file attach)

But Now i have a big problem..when a user reply, the reply moltiply

http://professionet.it/forum/discussioni/varco-pedonale-su-giardino-pubblico (see reply of ingmotty)
Why?!?!!

If you just want to remove the contents, then you just need to remove the $postContent from the email template.

As for the duplicate, I am not too sure what went wrong but I am assuming that the user pressed the submit button multiple times. Are you able to reproduce this issue?