Making Things Talk

92 MAKING THINGS TALK

How Email Works

Transferring mail also uses a client-server model. It

involves four applications: your email program and your

friend’s, and your email server (also called the mail host)

and your friend’s. Your email program adds a header to

your message to say that this is a mail message, who the

message is to and from, and what the subject is. Next, it

contacts your mail server, which then sends the mail on

to your friend’s mail server. When your friend checks her

mail, her mail program connects to her mail server and

downloads any waiting messages. The mail server is online

all the time, waiting for new messages for all of its users.

The transport protocol for mail is called SMTP, the Simple

Mail Transport Protocol. Just like HTTP, it’s text-based, and

you can use it from a command line. When a mail server

delivers a message, it has to figure out which servers are

responsible for handling incoming mail (for example mail.

example.com or smtp.example.com).

If you’d like to find the name of these servers, open

a command window/terminal program, and use the

nslookup command with the -q=mx option (this looks up

the mail server for the domain you specify):

C:\ >nslookup -q=mx gmail.com

Server: Unknown

Address: 192.168.254.1:53

Non-authoritative answer:

gmail.com MX preference = 50, mail exchanger = gsmtp163.google.com

gmail.com MX preference = 50, m