SMTP (Simple Mail Transfer Protocol) is used to transfer email between servers over the Internet. It is a push protocol that allows email clients to send messages to SMTP servers, which then forward the messages to their destinations. SMTP uses port 25 and involves establishing a TCP connection between a client and server, with the client sending commands and the server sending responses to transfer the message.

1. Simple Mail
Transfer
Protocol
(SMTP)

2. Simple Mail Transfer
Protocol (SMTP)
Email is emerging as the one of the most valuable service
in internet today. Most of the internet systems use SMTP
as a method to transfer mail from one user to another.
SMTP is a push protocol and is used to send the mail
whereas POP (post office protocol) or IMAP (internet
message access protocol) are used to retrieve those mails
at the receiver’s side.
Runs in port number 25

3. SMTP Fundamentals
SMTP is an application layer protocol. The client who wants to
send the mail opens a TCP connection to the SMTP server and
then sends the mail across the connection. The SMTP server is
always on listening mode. As soon as it listens for a TCP
connection from any client, the SMTP process initiates a
connection on that port (25). After successfully establishing the
TCP connection the client process sends the mail instantly.
SMTP Protocol
The SMTP model is of two type :
 End-to- end method
 Store-and- forward method

4. The end to end model is used to communicate between
different organizations whereas the store and forward
method is used within an organization.
A SMTP client who wants to send the mail will contact the
destination’s host SMTP directly in order to send the mail
to the destination. The SMTP server will keep the mail to
itself until it is successfully copied to the receiver’s SMTP.
The client SMTP is the one which initiates the session let
us call it as client- SMTP and the server SMTP is the one
which responds to the session request and let us call it as
receiver-SMTP. The client- SMTP will start the session and
the receiver-SMTP will respond to the request.

6. SMTP Process
 Contact server on well known port 25
 ASCII oriented command/response
 methodology
 contact server
 wait for greeting
 send HELO
 wait for response
 send command
 wait for response
 repeat last two

7. Remote Procedure Call
A remote procedure call is an interprocess communication technique that is used
for client-server based applications. It is also known as a subroutine call or a
function call.
 A client has a request message that the RPC translates and sends to the server.
This request may be a procedure or a function call to a remote server. When
the server receives the request, it sends the required response back to the
client. The client is blocked while the server is processing the call and only
resumed execution after the server is finished.
The sequence of events in a remote procedure call are given as follows:
 The client stub is called by the client.
 The client stub makes a system call to send the message to the server and
puts the parameters in the message.
 The message is sent from the client to the server by the client’s operating
system.
 The message is passed to the server stub by the server operating system.
 The parameters are removed from the message by the server stub.
 Then, the server procedure is called by the server stub.

9. ping
 Ping is a basic Internet program that allows a user to verify that a
particular IP address exists and can accept requests.
 Ping is used diagnostically to ensure that a host computer the
user is trying to reach is actually operating. Ping works by
sending an Internet Control Message Protocol (ICMP) Echo
Request to a specified interface on the network and waiting for a
reply.
 Ping can be used for troubleshooting to test connectivity and
determine response time.

10. Example..

11. netstat
 Netstat is a common command line TCP/IP networking utility
available in most versions of Windows, Linux, UNIX and other
operating systems.
 Netstat provides information and statistics about protocols in use
and current TCP/IP network connections.
(The name derives from the words network statistics.)
 The Windows help screen (analogous to a Linux or UNIX man
page) for netstat reads as follows:
 Displays protocol statistics and current TCP/IP network
connections.
Eg: - NETSTAT -a -b -e -n -o -p proto -r -s -v interval

12. Traceroute
Traceroute is a utility that records the route (the specific gateway
computers at each hop) through the Internet between your computer
and a specified destination computer.
It also calculates and displays the amount of time each hop took.
Traceroute is a handy tool both for understanding where problems
are in the Internet network and for getting a detailed sense of the
Internet itself.

15. Ipconfig
 Displays all current TCP/IP network configuration values and
refreshes Dynamic Host Configuration Protocol (DHCP) and
Domain Name System (DNS) settings.
 This command is most useful on computers that are configured
to obtain an IP address automatically. This enables users to
determine which TCP/IP configuration values have been
configured by DHCP, Automatic Private IP Addressing (APIPA),
or an alternate configuration.