How to explicitly allow incoming from select 'insecure' hosts?

[NaughtyusMaximus]

Hi,
I've set up 'max' security on my server, and there are a few clients who are no longer able to send email to me, since they haven't set up the same level of security that my server is now requiring. Is there a way that I can explicitly allow email from some select domains without lowering my security checks for all domains?

For example, this is an excerpt from my daily mail log:

Helo command rejected: Host not found (total: 657)
625 somedomain.com
14 mail5.somedomain.ca
...

I've added the domains I want to allow to my SpamAssassin conf, but I guess I need to do something else too.