Fortimail External Port access

Hi

I have a Fortimail 200E appliance.

We want to configure its port1 as an external port which directly goes out to the internet.

Is there a way to restrict traffic on this external port on SMTP services.

I know we can restrict it on http, https, SNMP, Ping, but I want to confirm if there would be a way to restrict it on SMTP port.