Such lists are primarily used by threat actors for:
Using legitimate, aged email accounts to bypass spam filters when sending out malicious links.
Files with names like this are often themselves. Security researchers frequently find that tools or databases shared on underground forums are bundled with: 280K VALID MAIL ACCESS.rar
Allowing the original uploader to gain remote access to the researcher's or "leecher's" system. Risk Mitigation
Malware designed to steal the credentials of the person downloading the file. Such lists are primarily used by threat actors
This specific archive is marketed as containing 280,000 sets of credentials that have been verified ("valid") for IMAP/POP3 access. This means the credentials allow a third party to log directly into the victims' email accounts.
Use legitimate services to see if your email has appeared in known public breaches. Risk Mitigation Malware designed to steal the credentials
Ensure you are not reusing the same password across multiple platforms, especially your primary email.