[exim] Relaying/Transport Question

Here's what ive wrote on FreeNode #Exim ... No answers

<IpNextGen> Q. : Is there something i could add in the "configure" file
of exim to prevent email with a specific domain to be relayed if its not
from a specific host mask or if its not sent via the exim in question?
<IpNextGen> Situation : im being spammed by email that use falsy my own
domain... therefore spamassassin auto-whitelist them ( because i
configured it to do soo )
<IpNextGen> i know i could remove my domain from the white list. But if
there's another way @ Exim level.. i would appreciate

Thanks