TCP/IP Tutorial and Technical Overview - IBM Redbooks

address” on page 559. You can see that this form of addressing is closely related
to the Domain Name System concept (see 12.2, “Dynamic Domain Name
System” on page 453). In fact, the client SMTP uses the Domain Name System
to determine the IP address of the destination mailbox (see 15.1.2, “SMTP and
the Domain Name System” on page 565).
Table 15-2 lists some frequently used fields.
Table 15-2 Common SMTP header fields
Keyword Value
To Primary recipients of the message.
cc Secondary (carbon-copy) recipients of the message.
From The sender of the message.
Reply-to The mailbox to which responses are to be sent. This field is added by
the sender.
Return-path The addresses and route by which the sender can be reached. This
field is added by the final transport system that delivers the mail.
Subject A summary of the message being sent. This is specified by the
sender.
A sample header might appear as follows:
From: myEmail@mydiv.redbookscorp.com
To: “Your Email”
cc: “Your Boss”
Reply-To: myEmail@mydiv.redbookscorp.com
Subject: This is a sample SMTP header
Mail exchange
The SMTP design is based on the model of communication shown in Figure 15-1
on page 562. As a result of a user mail request, the sender SMTP establishes a
two-way connection with a receiver SMTP. The receiver SMTP can be either the
ultimate destination or an intermediate (mail gateway). The sender SMTP will
generate commands that are replied to by the receiver SMTP.
Chapter 15. Mail applications 561