When we used Sybari Antigen 8.x, we were able to Filtering > File and block
an attachment with a certain file extension from going out of the
organization (by applying the filter to SMTP Scan Job only), but still allow
it to be emailed within our organization.
I don't find it possible in ForeFront for Exchange SP1. I seem to be only
able to apply the filtering to "Transport Scan Job" which applies to all
email, including internal and external.

Is my assumption correct? Is there a way to block an attachment by file
extension only when it goes external?

Thanks.