All the data transfer on the internet occurs through the use of protocols. The most well-known protocols are IP (Internet Protocol) and HTTP (Hyper Text Transfer Protocol). SMTP is a part of the application layer on the TCP/IP Protocol and the abbreviation expands to Simple Mail Transfer Protocol.
The SMTP is responsible for moving your email across various networks to help it reach its final destination—Your Inbox. The SMTP works in tandem with the Mail Transfer Agent (MTA) so that your mail can be delivered to the correct email inbox.
What does SMTP really do?
In simple words, SMTP directs emails to the network it should move onto, in order to reach the correct inbox. This is done by providing sets of codes which can simplify the communication of messages between email servers. The SMTP breaks down the message into a simple block that servers can easily understand. The message then becomes a string of characters, separated by code words that denote the importance of the section.
The email software determines what those code words actually mean, and in turn, understand what the text encapsulated by it is supposed to do. It is then passed on to the next step so that it moves on its way to the inbox. SMTP can transfer only text, and not graphics or any other non-text characters. The encoding of non-text characters into text is done by Multipurpose Internet Mail Extensions or MIMEs. The ISP also relies on the SMTP to determine when the email limit has been reached.