Hello, Guyz today I’m going to show you some basic things of SMTP server, before that let’s look at what are the basic things on the SNMP protocol. SMTP in the sense Simple Mail Transfer Protocol which is an internet standard for electronic mail transfer protocol over the Transmission Control Protocol/Internet Protocol (TCP/IP).
There are three individual areas in an e-mail message.
- Address format: Under the address format, senders and receivers can be identified clearly, who is the sender or receiver and what is the domain of the received e-mail. (ex: firstname.lastname@example.org)
- Message content.
- Message delivery.
Normally the SMTP server is used port 25 for communication and SMTP is an application layer protocol. In SMTP client-server process, first the SMTP client initiate the connection by sending request for the server on a remote host, if the server is accepted the request, the e-mail sending process will be started. The following diagram explain how the e-mail process is done via the SMTP that has been defined by the SMTP protocol. The image below, show you the basic idea of “How the SMTP client and Server are functioning”.
In the connection established is done by the 3-way handshake between the client and the server. In the 3-way handshake, the client will send the SYN message to the server to initiate the connection, if the server is accepted the connection, it will send the ACK message with SYN message to initiate the connection with the server, then the 3-way handshake is completed. The image given below is shows the Client & Server communication over SMTP Protocol.
After 3-way handshake is completed the server sends a message to the client with 220 which is indicated that the server is ready for transact for sending e-mails. Then the client identify the message from server by HELO which is used to read messages.
Then the Message is sent to the server side and ACK is sent by the server to the client, after finishes the message sending, client side sends the QUIT message to the server side. Then both sides will be sent the FIN messages and ACKs for terminate the connections.
This is a brief description, how the message communication is functioning between the client and the SMTP server.