These lists often contain data from legitimate breaches, such as the one reported at BreachForums
A file named like this is typically a containing thousands of email addresses or "combo" credentials (email:password sets) specifically categorized by major providers like Gmail, Yahoo, Hotmail, and AOL.
Gmail has the best filtering system.
While Yahoo and AOL are distinct brands, they share underlying technology.
to check if your credentials have been leaked in recent breaches. Enable MFA: