[exim] How to use ratelimit for a domain

I have a rule that limits all out going emails:

warn ratelimit = 5 / 1m / per_rcpt / strict
    delay = ${eval: ${sg{$sender_rate}{[.].*}{} -\
    $sender_rate_limit }s

How to I do the same thing but only when sending to a domain like bellsouth.net <http://bellsouth.net/>?