What command should an administrator execute to check for an unauthorized email relay agent on a web server?

To check for an unauthorized email relay agent on a web server, using the command to connect to port 25 is appropriate because this is the standard port for SMTP (Simple Mail Transfer Protocol). SMTP is the protocol used for sending emails over the internet, and port 25 is typically where email relay services listen for incoming connections.

When an administrator executes the command to telnet to the web server's domain on port 25, they can interact with the SMTP service directly. This interaction allows the administrator to send commands and receive responses from the mail server. By doing so, they can assess whether the server is configured to accept or relay emails, which would indicate the potential for unauthorized relay activity.

Unauthorized email relays can be a significant security concern, as they allow spammers to use the organization’s email infrastructure to send unsolicited emails, often leading to being blacklisted or experiencing increased spam filtering issues.

Other choices would not appropriately assess email relay capabilities; for instance, connecting to port 23 is related to Telnet, which is not relevant to SMTP operations, while connecting to port 80 corresponds to HTTP web traffic and does not provide useful information concerning email relay settings. Additionally, just specifying an IP without a port does not define the service being interacted