Bruno,
I seem to recall that there is a character limit (@150 characters) on the Forwarding Address field even though the form will allow you to put in more than that. Depending on the length of the email addresses you want to forward to you could get 3 (maybe even 5) email addresses before it gets functionally truncated. For Forwarders that need to go to > 3 recipients we have always setup an Alias instead of an Account to get around this. Aliases allow you to set as many addresses (one per line) as you want.