There are plenty of longer explanations of this online, but what you really want to know is "can you do anything about this"? Yes, but it can be difficult.
Emotional Support Animals are NOT Service Animals (service animals have specific training, ESAs do not), so they are not covered under the ADA. They ARE, however, covered under the Federal Fair Housing Act.
IMPORTANT POINT #1: If you are an landlord renting your own property without using an agent, and you have 3 or fewer rentals, you are not bound by the Fair Housing Act, so you can tell them to get stuffed. So when you're starting out, it's often better to handle your own rentals just for that reason.
IMPORTANT POINT #2: You do not have to accept an ESA letter from an online "Emotional Support Animal certification" site. Even HUD, bureaucrats that they are, recognize that most of those are BS. They allow you to require a letter from the person's own health care professional. So you can decline until they accommodate that. (HUD guidelines, see pg. 11).
IMPORTANT POINT #3: You can't turn down a Cane Corso just because it's a Cane Corso. But if you have evidence based on the behavior of the individual animal that it poses a danger to your property or to others, then you can disallow it. So the first time it threatens someone else, or if you see property damage during your regular site inspections or maintenance, you can make them get rid of it.
Good luck.