> Is it possible to ask Listserv to change the From: SMTP header (by default
> the sender E-Mail address) by a generic fix address ?

No, it is against standards to change the From: address.

> We would like to use
> Listserv (still in evaluation) to send internal NewsLetters. The senders of
> the Newsletters don't want to be importuned by user who want to reply to
> the list. We know there is the Reply-to directive that can be use. However,
> mailing list editors would like to hide their own name completly. Thank you
> for your help.

You would have to send the message From: an address you would want in the
From: field. This would not necessarily have to be an Editor's address
however. You could send it from another address and just have an Editor
approve it to the list. This is providing that address is not subscribed,
not an Editor or set to NOMAIL if subscribed.