Often referred to as an e-mail server, a device and/or program that routes an e-mail to the correct destination. Mail relays are typically used within local networks to transmit e-mails among local users. (For example, all of the student and faculty e-mail of a college campus.) Mail relays are particularly useful in e-mail aliasing where multiple e-mail addresses are used but the mail relay forwards all messages to the specified e-mail addresses to one single address.
A mail relay is different than an open relay, where an e-mail server processes a mail message that that neither originates or ends with a user that is within the server��s local domain (i.e., local IP range).