Blocking emails from a specific address

We've a mailing list allowing members of the public to contact the list members.  We've an ongoing issue with a particular person (not on the list) and would like to block emails from that address from going out to the list subscribers, but would like to specify a single address to which emails from this person will still get delivered - so that we can monitor the emails that they are sending.

Is this possible?
Will this person be aware that these emails are being blocked?

Thanks
Joe



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