Exercises

28.1	Read RFC 822 to find out what a domain literal is. Try sending mail to yourself using one .
28.2	Excluding the connection establishment and termination, what is the minimum number of network round trips to send a small mail message?
28.3	TCP is a full-duplex protocol, yet SMTP uses TCP in a half-duplex fashion. The client sends a command then stops and waits for the reply. Why doesn't the client send multiple commands at once, for example, a single write that contains the HELO, MAIL, RCPT, DATA, and QUIT commands ( assuming the body isn't too large)?
28.4	How can this half-duplex operation of SMTP fool the slow start mechanism when the network is running near capacity?
28.5	When multiple MX records exist with the same preference value, should they always be returned by a name server in the same order?