The paper (PDF) Email Security Issues, Tools, and Techniques Used in Investigation reviews real-world email forensic incidents and the tools used to mitigate threats.
Because these specific files are often associated with illegal activity (credential stuffing or hacking), formal academic papers do not exist for individual "MiX txt" downloads. However, you can find extensive research on the and forensic investigations related to these types of data breaches and email security. Relevant Research Papers & Resources Download Mail Access MiX txt
If you are researching this to protect your own accounts from being included in such lists, experts recommend: The paper (PDF) Email Security Issues, Tools, and
For a technical look at how organizations try to secure their domains, security.txt Revisited: Analysis of Prevalence and Conformity examines the adoption of standard security reporting methods. The paper (PDF) Email Security Issues