Now, email is emerging as one of the most valuable services on the internet. Presently, many of the online systems use SMTP as a procedure to send mail from one user to another. Now you can even buy SMTP with bitcoin. Primarily, SMTP is a push protocol and widely used to transmit the mail, whereas internet message access protocol or post office protocol are used to reclaim those mails at the receiver’s side. Moreover, the simple mail transfer protocol is also an application layer protocol.
The client who needs to send mail opens the TCP connection to an SMTP server and then transmits the mail across connection. However, this simple mail transfer protocol is continually on snooping type. As quickly when it snoops for the connection of TCP protocol as of any customer, the process of SMTP initiates the connection on such port (25). After successfully accomplishing the TCP connection, the client process transmits the mail immediately.
Working of SMTP
Composition of mail
The user transmits an email by just combining the automated mailing massage with help of Mail User Agent (MUA). Actually, the Mail User Agent is the platform that can be used to send and receive mail. This message normally consists of two parts such as body and header. The body is a major portion of the message, while the header includes information such as sender and recipient address. The header also adds descriptive information such as a subject of the message. In such case, the message body is like a header and a letter, which is like a wrapper that consists of recipient’s address.
Proposal of mail
After creating an email, the user of mail can submits the finalized email to a simple mail transfer server with the same SMTP on TCP port 25.
Delivery of mail
The email addresses consist of a couple of parts such as username of a recipient and a domain name. If the domain name of recipient’s email address is unique from the sender’s domain name. The MSA will transmit the email to the mail transfer agent. To relay this email, the MTA will discover a target domain. It also verifies the MX record from domain name system to get a target domain. The MX record consists of domain name as well as IP addresses of recipient’s domain. Once the record is placed, the MTA is linked to an exchange server to relay this message.
Receipt and processing of mail
Once the incoming message is received, the exchange server delivers it to the incoming server such as mail delivery agent that stores an email, where it waits for the user to recover it.
Entree and recovery of a mail
The saved email in MDA can usually get back with help of mail user agent. This agent can also be retrieved with the use of particular login and password.
Therefore, the main purpose of SMTP is used to set up the communication instructions between the servers. The servers also have a method of finding themselves and announcing what type of communication they are attempting to do. The SMTP also has a method of handling the faults such as incorrect email address.