The user nor I can send Internet mail to firstname.lastname@example.org. You do not have permission to send to this recipient. For assistance, contact your system administrator is returned with the NDR. Our Exchange server is not setup to deny Internet email. The person exists because the user has talked to that person and that person gave the user their email address. I checked with the user to make sure the email address was correct and they said yes. Is the error being generated from the recipients mail server, possibly due to some sort of blacklist?