[exim] How to use ratelimit for a domain

[William Dorrell]

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/>?
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