Set Default "From" address for email sent through Chatter Feed

I've created an Organization-Wide Address (Corporate CC) and I want this email to be the default "from" address when an operator send an email through the case Chatter Feed

as you see from the image, I can see "Corporate CC" in the "From" droplist, but the default is the email of the current User (User User). I tried, like someone suggested, to add the same address to the Feed View "Specify From Address(es)" configuration but still doesn't work.