Smarthost question

Hi Im trying to setup a smarthost. Im trying to setup a very similar mail routing topology like shown in the domino admin 6.5 help (if you search for “Example of using a smart host”).

If you look at that diagram my question is. If someone sends a mail from Mail1 to a user in the local internet domain that does not have a person document. Does the mail get sent to the smarthost VIA Mail2 or directly.

I would like to have only Notes routing between the domino servers and only SMTP routing between Mail2 and other domains.

Is this possible? What kind of configuration do I need to achieve this or can one only route mail to a smarthost via SMTP (ie between Mail1 → Mail2 → smarthost…)

Many Thanks…