SMTP OVERWIEW

A. Protocol Overview
In information technology context, protocol means a communications standard between systems or computer in a network. With existence of protocol hence a data can be transmission to destination node and after that, hence the data is acceptable truly. This communications procedures is very complex, include of errors way to overcome, way of sending data, way of the source gives information that data was transmitted successfully and also how the destination knows that data was accepted.

Protocol can be divided two kinds, that is:
• Low-level of protocol
This protocol determines data transmission rule from electronic side and physical, for example rule about bit and byte ordering, mechanism of error detection and corrective of errors. Example of this protocol is TCP/IP (Transfer Control Protocol/Internet Protocol).
• High-level of protocol
This protocol is responsible with data format, for example like syntax from message sent, message sequence sent (handshaking) and set character applied. Examples from this protocol are SMTP and POP3 for e-mail, HTTP for web browsing and FTP for transfer file and others.

Protocol should have the character of standard that can be applied by all sides. At internet community is recognized which named RFC (Request For Comment). RFC is a kind of documents containing rule protocol, which has become standard and or which still in phase experiment or draft. All protocol standards in internet always is written documentary of RFC and given by certain number.

In general communications protocols of TCP/IP (Transport Control Protocol/Internet Protocol) is divided into four layer:
1. Application Layer
The most widely known and implemented TCP/IP application layer protocols are File Transfer Protocol (FTP) which performs basic interactive file transfers between hosts, Telnet which enables users to execute terminal sessions with remote hosts, Simple Mail Transfer Protocol (SMTP) which supports basic message delivery services and Hypertext Transfer Protocol (HTTP) which supports the low-overhead transport of files consisting of a mixture of text and graphics.
2. Transport Layer
In TCP/IP architecture, there are two Transport Layer protocols. The Transmission Control Protocol (TCP) guarantees information transmission. The User Datagram Protocol (UDP) transports datagram without end-to-end reliability checking. Both protocols are useful for different applications.
3. Internet Layer
The Internet Protocol (IP) is the primary protocol in the TCP/IP Network Layer. All upper and lower layer communications must travel through IP as they are passed through the TCP/IP protocol stack. In addition, there are many supporting protocols in the Network Layer, such as ICMP, to facilitate and manage the routing process.
4. Network Access Layer
This layer is the lowest layer in TCP/IP architecture. This layer is responsible for actual transmission of data over the physical transmission media.

B. Definition SMTP
SMTP (Simple Mail Transfer Protocol) is one of protocol used occasionally for delivery of electronic mail in Internet. This protocol utilized to send data from electronic mail consignor computer to acceptor electronic mail server.This protocol arising from electronic mail system design obliging existence of electronic mail server accommodating temporary until electronic mail taken by acceptor which [is] entitled.
C. How does SMTP work
Basically e-mail sent by SMTP server will be accommodated temporary by server computer to be sent to server computer destination. Sender server computer and interaction acceptor server computer at port 25 to deliver of e-mail.

Logic give accepted e-mail is as follows:
For example there is user with e-mail address: dinand@dinanad.com wish to send e-mail to nando@nondocom from e-mail client. When dinand@dinandcom sends e-mail to nando@nandocom happened things following:
1. Enamel client does communications with akucom to apply port 25.
2. Enamel client communicates with SMTP server, advises to SMTP server about return address and acceptor, in parallel with contents of message sent.
3. SMTP server takes address purpose and divides it becomes two parts, that is :
• First part : nando
• Second part : nando.com
4. SMTP server does communications with DNS ( Domain Name Server) and asks address IP from kamu.com.
5. After IP is got, SMTP server dinand.com communicates with STMP server kamu.com to apply port 25, by the way of which same done between enamels client with SMTP server aku.com.
6. After message steps into server machine nando.com, user nando@nando.com can see e-mail message, for example with POP3.
this is process sending enamel with smtp server:
http://www.wiwid.org/html/images/stories/email_007.gif

Protocol Overview

In information technology context, protocol means a communications standard between systems or computer in a network. With existence of protocol hence a data can be transmission to destination node and after that, hence the data is acceptable truly. This communications procedures is very complex, include of errors way to overcome, way of sending data, way of the source gives information that data was transmitted successfully and also how the destination knows that data was accepted.

Protocol can be divided two kinds, that is:
1.Low-level of protocol
This protocol determines data transmission rule from electronic side and physical, for example rule about bit and byte ordering, mechanism of error detection and corrective of errors. Example of this protocol is TCP/IP (Transfer Control Protocol/Internet Protocol).
2.High-level of protocol
This protocol is responsible with data format, for example like syntax from message sent, message sequence sent (handshaking) and set character applied. Examples from this protocol are SMTP and POP3 for e-mail, HTTP for web browsing and FTP for transfer file and others.

Protocol should have the character of standard that can be applied by all sides. At internet community is recognized which named RFC (Request For Comment). RFC is a kind of documents containing rule protocol, which has become standard and or which still in phase experiment or draft. All protocol standards in internet always is written documentary of RFC and given by certain number.


In general communications protocols of Open System Interconnection applied is divisible in seven protocols, there are:
a)Physical layer.
The lowest layer in the form of communications channel hardware applied. This peripheral cans be in the form of telephone channel, communications radio-set, modem peripheral and computer.
b)Data Link layer.
This layer is arranging the communications between two computers. This protocol only arranges delivery of data between two computers through the physical layer.
c)Network layer.
This protocol controls the relationship between computers in network which connected many computers. For example, find the route relation between one computer to other computer assisted by this protocol.
d)Transport layer.
This protocol is responsible of delivery reliability of data out of one computer to other computer in network.
e)Session layer
The session layer establishes, manages and synchronizes the communication between two communicating computers
f)Presentation layer
This layer encodes and decodes data in a mutually agreeable format. This layer also compresses and decompresses data packets.
g)Application layer
Application layer provides an interface between the user and the network. Some of the common application on this layer is Telnet, file transfer of protocol (FTP).

Although theoretically there are seven protocol layer, practically not always all levels applied by network. At some a real computer network techniques complicated protocol layer layer simple generally is not applied, and application program directly joined with others at physical layer.
By : Ferdinan

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