What server facilitates communication between two email servers?

The correct answer is a mail server. A mail server is specifically designed to facilitate the sending and receiving of email between different email servers. When an email is sent, it first goes to the sender's mail server, which then communicates with the recipient's mail server to deliver the message. This process involves various protocols such as SMTP (Simple Mail Transfer Protocol) for sending and IMAP (Internet Message Access Protocol) or POP3 (Post Office Protocol) for receiving emails.

The other options do not serve this purpose. An FTP server is used primarily for transferring files over the Internet, a print server manages printers and print jobs within a network, and a web server hosts websites and serves web pages to users. Each of these servers has distinct functions that do not involve direct email communication between servers, highlighting the unique role of the mail server in facilitating email exchange.