SMTP stands for Simple Mail Transfer Protocol and it is a format widely used mainly for sending emails. Most client mail applications typically use SMTP for sending messages to a mail server for further relaying. Most often for receiving messages, a client application will use either the Post Office Protocol (POP) or the Internet Message Access Protocol (IMAP). Both are fairly common with internet service providers and most e-mail handling applications can be set up to use any combination of these common protocols.
The basic definition for SMTP goes as far back as the early 1970’s when it was called Mail Box Protocol. At the time, there were only about 50 total hosts on what was then known as ARPANET, the precursor to what we know as the internet. SMTP became widely used in the 1980’s and was most useful for when machines were connected to the internet full time. Originally it was only set up to handle raw text using the standard ASCII character set, but later refinements were made to include binary files such as images.