OK. FTR, the better way to whitelist is to allow only email that's signed with your DKIM key. This signature can't be forged and doesn't depend on a specific IP address.
They may not have the technical ability to do this, however.
Yes, at Marketo we block mail to both full email addresses and domains in some cases. We may add the full email address to our global blocker for someone who has requested to receive no mail from Marketo customers. We often will get these requests to firstname.lastname@example.org. And, if we identify a domain that is being used as a spam trap or other area that is risky to send to we will block the full domain from receiving mail.