title: Why 2 different servers (incoming and outgoing) in mail servers?
body: <p>I have a basic question about mail servers. Usually any general server (not necessarily mail servers)  handle all kinds of related requests i.e. both direction interaction with client (like sending and receiving msg to and from client) but  in case of mail servers, there are 2 different servers -- one for outgoing messages called outgoing server following SMTP protocol and another for incoming messages called incoming server following POP3/IMAP protocol. Why so? . For that matter couldn't the 2 protocols be accommodated in one single protocol to handle both direction message flow. Also, typically are these 2 servers hosted on same machine in a general business?</p>