Breach Checker: Email breach search
Breachchecker is a very user friendly web app that allows you to check not only if an email was breached, but what breaches it was included in. It also lets you know when the leak occured to give you a timeline of events. This can help you determine how old an email was. If you're finding breaches from before 2016, for example, you know the owner of the email has had it for a long time. Likewise, if you find the email breached from companies that either weren't large or didn't exist after 2016 (in this example), you can assess how actively used an email is.