[exim] Restricting mail to internal mailing lists.

My employer is using exim 4 as for our smtp gateway server. We wish to stop
spammers from sending to our internal mailing lists, e.g.
allstaff@???, payroll@???. However, we wish some of
our partners and customers to be able to send to said list.
For instance, inbound mail from jdoe@???, *@partner2.com, and
jdoe@??? should be allowed to send to our internal mailing lists.

How do can I make this happen?



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Cheers,
Conrad