SMTP Simple Mail Transfer Protocol

In this article I describe the SMTP Simple Mail Transfer Protocol in computer network for CCNA Exam. SMTP Simple Mail Transfer Protocol provide to send or forward the email messages from client to mail server. Sometime mail server to mail server email sent by using the SMTP Simple Mail Transfer Protocol. A client can send the email messages to mail server via using the SMTP Simple Mail Transfer Protocol.

SMTP Simple Mail Transfer Protocol works between the client and the mail server as well as between mail server to mail server on internet. Some private organizations uses their own private mail services on the intranet. I mean to say the mail server and client communicate over the internet but in the way of intranet. Before going to learn about the SMTP Simple Mail Transfer Protocol let’s take a look on some basic terms related to email services.

History or Email

According to some computer magazines and other resources, the first email was sent from one computer to another computer in 1971. The engineer who supposed to be sent first email was RAY TOMLINSON. Before this event an user can sent the message within a single machine with some standalone applications. After the mail sent within different machines the email creates a revolution in the field of Information Technology. Now there are many email servers available like Microsoft exchange server, IBM’s Lotus and many other of Linux version.

The Email system in computer network or internet

Email is generally pronounced in place of electronic mail. An Email provide to share text, graphics, audio and video from a user to another user on internet. Approx. 80% people around the world works on email on internet. People use email to send personal information as well as official information on internet. Email services provided by some particular Email servers for clients. The clients are the users created in email servers to provide the email services. The connectivity between the clients and mail server may be on internet or intranet.  

An email can be configured on a domain name with prefix the email address for example user_name@domain_name. multiple protocols required to float an email address from sender to receiver. The main protocols are IMAP, SMTP and POP3 which are used for floating the email on a network. In this article our focus is on SMTP Simple Mail Transfer Protocol which is used to forward the emails towards mail servers. Later in this article you will know the difference between forwarding mail from client to server and from server to client.

Email servers in mail services

Email servers are liable to receive, forward, deliver and store the emails between the email users. The email message can be downloaded by the clients or a client can access the email messages from the mail server on browser based. The email server deliver the mail to the recipient, in case the recipient is not available, the mail server notify the mail sender about the failure of delivery of email. Mail servers are generally of three types SMTP servers, POP servers and IMAP servers. All three severs have different kind of works. Forwarding and receiving of email are depends on the email services.

Email Clients in mail services

Email clients related to the user who is using the email service. Actually the email client is a software which is configured to receive the email and restore the mails in it. A user can see the emails by just opening the email client software. The examples of mail clients are thunderbird, outlook etc. All smart phone provide a facility to configure the mail server. The email server provides the data so a user can configure his smart phone as email client. What happens now, when the smart phone get internet connection the mail application receive the email from the mail server. The user can read the mails any time once after the email received by the mail application.

Webmail interface for email

The webmail interface allow a user to access the email account from a browser of a computer or smartphone. The computer or smart phone must be connected to the network or internet. The email appears and can be forwarded till the browser is open. Once the browser closed the email access is vanished. So this is the most common technique via which most of email users access their mail accounts from the internet. Later in this article i describe the protocols used when a client access the email from a browser of a computer.

Protocols used for email service

There are three protocols used for email service on the internet POP3 Post Office Protocol, IMAP and SMTP Simple Mail Transfer Protocol. SMTP Simple Mail Transfer Protocol use to forward the email while remaining two POP3 and IMAP used to retrieve or receive the email from the mail server.

POP3 Post Office Protocol allow to download the email in a computer client or smart phone. After downloading the email the mail server delete the delivered emails. So by using POP3 Post Office Protocol a user can read the emails only on a single device. Once the email downloaded into the mail client the mail automatically deleted from the mail server. POP3 Post Office Protocol works on port 110 and 995.

Port 110 used for insecure like HTTP and 995 is used for secure mail communication like HTTPS. POP3 Post Office Protocol saved the emails in mail server’s single mailbox. The saved email sent to the user when mail client opens. If you want to access your email form one machine and the machine have a lot of space, then POP3 protocol is useful to you. POP3 Post Office Protocol doesn’t support multiple device for same user.

IMAP Internet Message Access Protocol is another protocol to retrieve the emails from the mail server. Mostly the IMAP Internet Message Access Protocol allow to access the email on browser based access from a computer or client. The difference of IMAP from POP3 Post Office Protocol is that IMAP allow to access the emails from different applications and clients. Hence a user can access his email from multiple device and applications when using the IMAP Internet Message Access Protocol. Now lets see the POP3 Post Office Protocol in brief.

SMTP Simple Mail Transfer protocol provide the feature to send the email from one client to another client over the internet. SMTP Simple Mail Transfer Protocol works on port 25, 2525 and 465. Port 25 and 2525 works to send the email without encryption and port 465 used to send the email securily on internet or WAN.

SMTP Simple Mail Transfer protocol explained

SMTP Simple Mail Transfer Protocol is an application layer protocol. SMTP Simple Mail Transfer protocol used for sending email message between client and mail server. The SMTP used to transfer the mail message from a mail server to another mail server. Email within a network or internet sent via SMTP Simple Mail Transfer protocol. SMTP is a push protocol. Three protocols used for Email transfer from one user to another user.

The three protocols used for emailing are SMTP Simple Mail Transfer Protocol, POP post office protocol and IMAP internet message access protocol. Email server receive the mail message from any client or other mail server by SMTP Simple Mail Transfer Protocol always.

SMTP Simple Mail Transfer Protocol Basic Concepts.

SMTP Simple Mail Transfer protocol used by all mail servers to receive and sent the mail message. SMTP is an application layer protocol. Email sent via SMTP Simple Mail Transfer protocol over the TCP/IP connection.

Port 25 is used in TCP connection by SMTP Simple Mail Transfer Protocol. The SMTP server is always remaining on listening mode. When there is any email requesting to be forwarded the Simple Mail Transfer protocol allowed the email to forward towards the email server. Later the client can retrieve the forwarded email by using IMAP or POP3 protocol.

Types of SMTP Simple Mail Transfer Protocol

Simple Mail Transfer protocol is of two types in computer networking. One is End-to- end and another is Store-and- forward method. End-to-End method is use between different organizations. In End-to-End method the client send the email for another client. The email sent from one client to another client via some mail servers as shown in figure. All three protocols works during the complete transmission of the email from client to another client.

Store-and-forward method used within a network or organization. Simple Mail Transfer protocol server keep the mail in its mailbox until the mail is deliver to the receiver client. After successful copy of the email message in client’s mailbox, the email message is deleted from the mail server. The administrator or mail server can define the life span of an email in the mail server.  

Important specifications of SMTP Simple Mail Transfer Protocol

SMTP is connection oriented and text-based protocol. SMTP has a provision to indicates about incoming mail. The SMTP transfer the email message on the TCP/IP network. When message not delivered successfully, A report about it is sent to the sender to resend the email message.

Examples of some SMTP Commands

HELLO command begins the conversation of SMTP over the TCP/IP network. EHELLO is an alternative command to HELLO. EHELLO command also begins the conversation of SMTP. ESMTP command is use to intimate to use extended SMTP protocol. MAIL FROM command tells about the mail message sender address. RCPT TO command is use to identifies the recipient address of email message. SIZE command intimates the size of attached message in bytes to the sender server. DATA command indicates that a data stream will follow. QUIT command is used to terminate the SMTP connection in a TCP/IP network. VERIFY command is use by the receiving server.

In this article I describe the SMTP Simple Mail Transfer protocol in computer network for CCNA Exam. I hope you found this article helpful. For any query or suggestion on this article you may drop a comment below or contact us. Your suggestions are always welcome by us.