[Exim] "Secure" relay from a host

Hi,

Apologies if this gets asked often, I couldn't see it in the
archives but AFAICT there's no search.

Is it possible to relay mail from a host *only* if the Envelope
sender matches a certain pattern? (Specifically, *@some.domain)

Thanks.

-- 
Ryan O'Connell - On:Line Finance IT Department - <ryan@???>
                 NOC/Support Voice Line: +44 1932 235320

You are the Dancing Queen, young and sweet, only seventeen
Dancing Queen, feel the beat from the tambourine
You can dance, you can jive, having the time of your life
See that girl, watch that scene, dig in the Dancing Queen