Email is much older than internet. It was never invented but evolved from simple start. The Email left behind much like leaving a note on someones desk and the message would seen by user later.
The first email system was probably the MAILBOX which was used at the Massachusetts Institute of Technology in 1965. SNDMSG was another early program which was used to send messages on the same computer. This email messaging on same computer happened before the arrival of internet.
With the arrival of internet, there was a problem of making sure the message was sent to the right person and identifying the exact person to receive the email message was much more complicated.
Ray Tomlinson invented the email message addressing in 1972. The symbol @ was chosen for sending messages from one computer to another. For any Internet user since that time,, addressing the email was as simple as nominating name-of-the-user@name-of-the-computer. The additional features like sorting and labeling emails in folders came much later.
During the early times, connecting to the internet was expensive. There were also demerits in the keyboard functions which annoyed the email users. There was concept of offline readers that allowed users to store their emails in their personal computers. The emails could be read and replied could be prepared without getting connected to the internet. This was similar to todays MS Outlook.
With the advancement in technology, the features of email progressed from basic to sophisticated. Standard protocols were developed. One of the first important standard protocols was SMTP or Simple Message Transfer Protocol. Another standard protocol is called POP or Post Office Protocol.
Both SMTP and POP were important configurations for email clients such as the Microsoft Outlook to download email from the server and to send email through the server using a desktop program.
Nowadays, Besides Hotmail and Gmail, there other many other popular websites which offer email services.