Simple Mail Transfer Protocol (SMTP)

                                          Simple MailTransfer Protocol (SMTP)

SMTP is a simple ASCII protocol for transferring mail between hosts in the TCP/IP suite. After establishing the TCP connection to port 25, the sending machine, operating as the client, waits for the receiving machine, operating as the server, to talk first. The server starts by sending a line of text giving its identity and telling whether it is prepared to receive mail. If it is not, the client releases the connection and tries again later. If the server is willing to accept email, the client announces whom the email is coming from and whom it is going to. If such a recipient exists at the destination, the server gives the client the go-ahead to send the message. Then the client sends the message and the server acknowledges it. No checksums are needed because TCP provides a reliable byte stream. If there is more email, that is now sent. When all the email has been exchanged in both directions, the connection is released.

Simple Mail Transfer Protocol (SMTP) is a formal protocol that defines the message transfer agents (MTA) client and server in the Internet. When the message is send to a mail server, it uses the SMTP to send that mail in receiver’s server. When the message arrives at the destination server, it is then uses POP or IMAP to download the mail from the incoming server. Hence, SMTP is message transfer agent and POP & IMAP are message access agent.

Post Office Protocal(POP)	Internet Messadge Access Protocol (IMAP)
1. When you open your mail box, new mails is moved or downloads permanently from host server & saves on your computer. Hence, if you want to see your previous e-mail, you have to go back to the previous computer where you last open your mail.	1.The mail is permanently stored in the server until you delete this. Thus, you can access them from various locations & various times.
2.With POP you have only one folder, index folder, in the mail-server.	2. Mail stay on the server in multiple folders, some of which you have created.
3.User cannot access his multimedia e-mail if he has limited bandwidth.	3. If limited bandwidth is available then a user can partially download e-mail contents.
4. POP has only two modes i.e. keep mode & delete mode for message.	4. A user can create, delete or rename mailboxes on the mail server.
5.Message storage limited only by the capacity of your computer, but if your computer fails; you may lose all your messages.	5. The message storage capacity is limited to 2GB & there is no any affect if your computer fails.
6.Reading your e-mail from multiple computer results the message scatterings.	6.Easily can use the multiple computers or e-mail program to read same mail as it is stored in the mail-server.