Hello @TonyC06056 ,
Thank you for reaching out about this. Because of how many contacts you have, you will not have the limit option you're looking for. However, there is still a way to do this!
You'll want to start by merging lists A and B into a new list. Once that is complete, you'll go into List C and remove that from the newly merged list, leaving you with Lists A and B minus C.
Then you'll be able to send your email to your new list!
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