You are welcome
>
> I have not used ACL's before so I please confirm this
>
> deny
> !hosts = 1.2.3.4 [Is this the antispam gateway IP?]
Indeed, this is the name or the IP of the antispam gateway. You don't
want to reject the mails coming from there.
> domains = dom1.tld : dom2.tld [Domains I want to restrict?]
You are right.
> message = Your mail must be sent through the antispam gateway
>