Yet another "disable outgoing scan" question

[Mauricio Tavares]

      As the subject states, I would like to disable outgoing scan.
Now, from what I saw in mailscanner.conf and was explained in the irc
channel, I should set Scan Messages = my ruleset file and then have
something like

From:     my.domain.com no
FromOrTo: default           yes

in the file. Question I have is would the first line cause emails
pretending to be coming from my domain not to be scanned? If so, how
would I make sure only the emails that truly originate from my domain
not be scanned?