Simple Mail Transfer Protocol (SMTP)
Simple Mail Transfer Protocol (SMTP) is present in the application layer of the TCP/IP. It is used to send and receive e-mail using a store and forward mechanism. SMTP moves your email across networks. It works with the Mail Transfer Agent (MTA) to send the email to the right inbox. It basically tells the email how to move from the client’s MTA to the server’s MTA. The message moves step by step from source to destination by the help of SMTP. A user luckily does not need to understand how to operate SMTP. It all takes place behind the scenes.
Part -2
Protocols are needed to perform almost all the online activity. Protocols are rules that allow a device to link with networks everywhere. SMTP is one of these protocols that helps us to send emails. It provides a set of codes that simplify the sending of messages from the email server. An Email server is a network computer that handles outgoing and incoming email. SMTP can transfer texts. It cannot handle graphics, attachment, fonts, etc. Hence the name Simple MTP. Thus, MIME (Multipurpose Internet Mail Extensions) was created to encrypt non-text content in plain text. Then SMTP is used to transfer the data.
SMTP breaks up different parts of the message into categories understood by the server. The email we send is converted to strings of texts separated by code words to identify various sections of the message. SMTP’s job is to provide these codes to the email server. The server has a software that can understand the meaning of these strings. The message passes via a number of computers and MTA’s before it reaches its destination. It gets stored briefly. Before being passed on to the next computer in its path. The process is similar to a letter that goes to different hands before reaching the correct mailbox.
SMTP has limited ability to queue messages at the receiving end. It, therefore, uses IMAP (Internet Message Access Protocol) / POP3 (Post Office Protocol 3) to save messages on the server mailbox and download them from the server. Hence SMTP is used to send email whereas POP3 or IMAP are used to receive email. SMTP sends emails from the mail client to mail server. Hence we need to specify SMTP and POP/IMAP while configuring the email application.
On a Unix based system. Sendmail is used as an SMTP server for email transfer. Sendmail includes POP3 server as well. Microsoft Exchange also includes SMTP server and can be set up to include POP3 as well. SMTP operates on the Internet port 25. In Europe, an alternative to SMTP is used. It is called X.400. X.400 was the standard for sending and addressing emails in 1984. It was expected to become what SMTP is today, but SMTP took over after a few years. It was mainly due to SMTP’s simplicity over X.400. X.400 even charged for sending emails while SMTP as we know is absolutely free. Mail services these days widely support ESMTP (Extended Simple Mail Transfer Protocol) that allows multimedia files to be sent as email.
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