What type of server maintains an access log to assist with troubleshooting and tracking down malicious users?

The type of server that maintains an access log to assist with troubleshooting and tracking down malicious users is the file transfer protocol (FTP) server. FTP servers are designed to handle the transfer of files over a network, and as part of their function, they maintain detailed logs of user access, including timestamps and the actions performed by users during their sessions. This logging capability is vital for identifying unauthorized access attempts, understanding usage patterns, and responding to security incidents.

While web servers, email servers, and database servers also maintain logs for various purposes, the specific reference to "file transfer" in the question highlights the role of an FTP server in managing detailed access records directly related to file transfers. This makes it particularly useful for troubleshooting issues related to file access, integrity, and potential security breaches.