Which of the following server types can be configured and joined to the existing network as a read-only server for user account verification to external websites?

A Syslog server collects log messages from various devices and is not involved in user account verification or authentication.

A web server hosts websites and web applications; while it might consume authentication services, it does not provide read-only user account verification for other external websites in this manner.

A directory server, often implementing protocols like LDAP (Lightweight Directory Access Protocol) or services like Active Directory Domain Services, stores user accounts and their authentication information. A read-only replica (e.g., a Read-Only Domain Controller - RODC in Active Directory) can be deployed to provide user account verification services to external applications or websites without allowing write access to the central directory, enhancing security.

A messaging server (like an email server) handles email communication and is unrelated to providing user account verification for external websites.