[exim] Verification Question

Trying to figure out how to do this. I want to do something like a
recipient verify but not verify the recipient. I want to attempty to
verify a fixed email address that should be an address that doesn't
exist so that I can tell if the recipient server takes wildcard addresses.

What I'm trying to do is figure whick of my customers allows wildcard
emails. But I can figure out how to test for a fixed email address
rather than the sender or recipient.