TCP 

transmission Control Protocol (TCP) is a standard that defines how to establish and maintain a network conversation by which applications can exchange data.

TCP works with the Internet Protocol (IP), which defines how computers send  of data to each other. Together, TCP and IP are the basic rules that define the internet

        SMTP

Email is emerging as one of the most valuable services on the internet today. Most internet systems use SMTP as a method to transfer mail from one user to another. SMTP is a push protocol and is used to send the mail.

     SMTP is an application layer protocol. The client who wants to send the mail opens a TCP connection to the SMTP server and then sends the mail across the connection.

The SMTP model is of two types:

1. end-to-end 

2. store and forward

      POP 3

The POP3 abbreviation stands for Post Office Protocol version 3, which provides access to an inbox stored in an email server.

   It executes the download and delete operations for messages. Thus, when a POP3 client connects to the mail server, it retrieves all messages from the mailbox. Then it stores them on your local computer and deletes them from the remote server.

    Modern POP3 clients allow you to keep a copy of your messages on the server if you explicitly select this option

      HTTP

The Hypertext Transfer Protocol (HTTP) is the foundation of the World Wide Web, and is used to load webpages using hypertext links.

    As a request-response protocol, HTTP gives users a way to interact with web resources such as HTML files by transmitting hypertext messages between clients and servers. HTTP clients generally use Transmission Control Protocol (TCP) connections to communicate with servers

      HTTP utilizes specific request methods in order to perform various tasks. All HTTP servers use the GET and HEAD methods, but not all support the rest of these request methods