While others pointed out that Have I Been Pwned is (kind of) for this specific purpose, there is a limit of like 10 email addresses. Beyond that, you will have to have a paid subscription. You'll still get "alerts" without the subscription, but have no way of seeing which email addresses have made it into a leak somewhere. And the pricing cliff was pretty steep if I recall correctly.

Minimum ~$50 / year for 1 domain and up to 25 breached email addresses. https://haveibeenpwned.com/Subscription

I'm just one guy, but I have a lot of project domains. If I wanted to monitor 5 domains, it would cost me $443 / year.