What is a mail server?
At the most basic level, an e-mail server is a mail transfer agent (MTA) and is responsible for moving an e-mail message from sender to recipient, most commonly employing Simple Mail Transport Protocol (SMTP) to deliver a message to the next server. An e-mail server may additionally host mailboxes, where e-mail messages are ultimately delivered, and so will respond to protocols designed for retrieving e-mail from mailboxes.
