Simple Mail Transfer Protocol (SMTP) is the standard protocol for sending email across the internet. SMTP was created in 1982 and uses a client-server model with user agents to prepare messages and mail transfer agents to reliably transfer messages between servers. An email consists of an envelope containing sender and recipient addresses, and a message with a header defining sender, recipient, subject, and a body containing the actual content. SMTP works by establishing a TCP connection between servers, sending commands like MAIL FROM, RCPT TO, and DATA to transfer the message, then terminating the connection. Extensions like MIME allow non-text content like images and files to be included in emails.

1. Simple Mail Transfer Protocol
Prepared By: Ali A. Obaid
Ramadhan S. Ramadhan
2017

2. Overview
 Introduction
 Message Breakdown
 Sending Messages
 Extensions
 Retrieving mail (Mailbox Protocols)
 Examples

3. Introduction
 Email (electronic mail) is a way to
send and receive messages across
the Internet. It's similar to traditional
mail.

4. Email Statistics
Email Statistics (2004):
 31 billion emails sent daily,
expected to double by
2006
 Email generates about one
billion Gigabytes of new
“information” per year
 Spam accounts for about
40% of all email traffic
http://www.spamfilterreview.com

5. SMTP
 Protocol originated in 1982 (RFC821, Jon Postel)
 Standard message format (RFC822,2822, D. Crocker)
 Goal: To transfer mail reliably and efficiently

6. SMTP
 SMTP clients and
servers have two main
components
 User Agents – Prepares
the message, encloses it
in an envelope. (ex.
Thunderbird, Eudora)
 Mail Transfer Agent –
Transfers the mail across
the internet (ex.
Sendmail, Exim)
 Analogous to the postal
system in many ways

7. SMTP
 SMTP also allows
the use of Relays
allowing other
MTAs to relay the
mail
 Mail Gateways are
used to relay mail
prepared by a
protocol other than
SMTP and convert
it to SMTP

8. Format of an email
 Mail is a text file
 Envelope –
 sender address
 receiver address
 other information
 Message –
 Mail Header – defines
the sender, the
receiver, the subject of
the message, and
other information
 Mail Body – Contains
the actual information
in the message

9. How SMTP works (A-PDU’s)
 The Basics
Keyword Arguments
HELO Sender’s Host Domain Name
MAIL
FROM:
Email Address of sender
RCPT TO: Email of Intended recipient
DATA Body of the message
QUIT

10. Connection Establishment
TCP Connection
Establishment

11. Message
Progress

12. Connection Termination
TCP Connection Termination

13. Solution: SMTP extensions
 MIME – Multipurpose Internet Mail Extensions
 Transforms non-ASCII data to NVT (Network Virtual Terminal)
ASCII data

Text

Application

Image

Audio

Video
RFC 1425, 1426, 1521

14. Any
Questions ?