Currently among the internet users, POP is not a new item. By using POP, someone gets easier to get his mail from a mail server, without the need to connect the old with the internet, of course, cost. Below, I will explain a little about the workings of the POP. In this paper, the term will be found many client and server. Client and server is part of the architecture that is widely used in the implementation of internet services. This architecture is commonly referred to as client / server architecture. Understanding POP3 client in a discussion about this is the party that uses the POP3 service and server is the party that provides services
Is it POP?
POP or Post Office Protocol, as the name suggests is a protocol for managing mail. POP is now more commonly known as POP3 (POP - Version 3), intended to allow the client to dynamically access mail that is still on the POP3 server. POP3 offers the user to leave mail on the POP3 server her, and took his mail from any number of systems. To retrieve mail using POP3 from a client, many options can be used such as Sun Microsystems Inc. 'S Mailtool, Qualcomm Inc.' S Eudora, Netscape Comm. Corp. 'S Netscape Mail and Microsoft Corp.' S Outlook Express.
POP3 is not intended to provide mail manipulation operations on the server extensively. On POP3, mail is taken from the server and then deleted (or may not be removed). Everything about the POP3 protocol is discussed in RFC (Request For Comment) 1725. Protocol is higher and more complex, that is IMAP4, is discussed in RFC 1730.
POP3 mode
There are two types of modes on the POP3 offline mode and inline mode. In the offline mode, POP3 mail retrieve and then delete the saved from the server. POP3 works fine in this mode, because it primarily was designed to act as a mail system that has the character of the "store-and-forward". Server, the offline mode, acting as a reservoir that holds the mail until the user requests it.
In the inline mode, will take mail from the POP3 server without deleting the mail that has been captured. This mode is preferred by users who often change places (nomadic user) because it allows them to see the same mail from a place or a different computer. However, for the nomadic user is always working and traveling always carry a notebook, and still wants his mail on the server are not deleted, of course, want to pick up mail every time the mail is not all that will be drawn, but only the mail that he had never just look at who will be taken. This user desires can be fulfilled by using the information on the client that allows to mark mail that has ever seen. Any client that supports POP3 service inline mode will store this information in a file. The users who use Netscape Mail, files that store this information is popstate.dat file, usually located in / Program Files / Netscape / Users / Mail. Mail the file to tell where it had taken so it does not need to be taken again. If the file is deleted then of course the decision-mail all mail will be drawn next. The contents of the file popstate.dat for a user who has logged such as 'Jim' on the POP3 server students.itb.ac.id are as follows:
# Netscape POP3 State File
# This is a generated file! Do not edit.
* Jim students.itb.ac.id
k c67ee091087ed814337b4cb31e0d488c
k 8541822a98e890b88d8299d034993f61
k 652e17a1c984e610e4e55257c07b6ff4
On this file the code behind the letter k is the unique-id. These unique-id uniquely identifies a mail in the maildrop so that each has a unique mail-id is different. If for example our mail in the local computer is deleted while we want to read it again, so before we take the maildrop from the server, file popstate.dat must be removed first. If we do not delete the file then there will be a message: "no new messages on server", which is given by the Netscape Mail. For Eudora users, files that store this information is lmos.dat file, whereas for Outlook Express users typically use pop3uidl.dat file.
Basic operation of POP3
At first, the server starts the POP3 service by listening to requests on TCP port 110. When a client requests the service, then there is a TCP connection to the server. At the time the relationship began, the POP3 server sends a greeting (opening words). After that the client will give the command (command) to the server and the POP3 server will give a response (answer) until the connection is closed or canceled. Keep in mind that the user does not enter this command, but the software of the client who sends this command to the server.
POP3 commands consist of a keyword is not case sensitive (capitalization does not question or not), which can be followed by one or more arguments. Keywords and arguments each separated by a SPACE character (space). Title consists of three or four characters, while each argument can be up to 40 characters. The answer in the POP3 consist of a status indicator and a keyword that can be followed by additional information. There are two status indicators: positive ("+ OK") and negative ("-ERR"). Server should provide the answer + OK and-ERR in capital letters. At a certain command, the server will give an answer that consists of several lines.
A POP3 session connection is built through three stages, namely stages of authorization, transaction and update. Once the TCP connection starts and the POP3 server has sent a greeting, then the relationship has entered a stage of the session authorization. At this stage the client sends the user name and password to the server for that user membuktian authenticity in order to retrieve his mail. When the client has managed to prove her identity, the server will obtain information relating to the mail client owned, and sessions are now entering the phase of the transaction. At this stage of a process of receiving mail, marking mail for deletion, cancellation marking for deletion, the appearance of the identity details of statistics mail or mail. By the time the client has quit command to end the relationship, then entered the stage of update sessions. At this stage the server will execute all orders obtained during the transaction and close the session and subsequent TCP connection is closed.
A server has to answer an unknown command, not implemented, or not in accordance with the syntax with a negative status indicator. The server also must provide a negative status indicator, if any client that provides commands that should not at this stage. There is no general method that can be used by the client to distinguish between the servers that do not implement the additional commands to the server that is unable or unwilling to process the additional orders.
A POP3 server may have autologout timer for client who is not active within a certain time frame. Timer like this should at least have a span of 10 minutes. If a server receives any command from the client within that time, then this is enough to reset the timer autologout. When the time span of the timer is up, with no activity from the client session does not enter the phase relationship UPDATE. Server will close the TCP connection without removing mail or send a reply to the client.
All messages are delivered during the session should be adjusted POP3 connection to the standard format of Internet text messages. Internet text messages this is discussed in detail in RFC 822. Table 1. below shows the commands in the following POP3 commands the stage where it is used.
Is it POP?
POP or Post Office Protocol, as the name suggests is a protocol for managing mail. POP is now more commonly known as POP3 (POP - Version 3), intended to allow the client to dynamically access mail that is still on the POP3 server. POP3 offers the user to leave mail on the POP3 server her, and took his mail from any number of systems. To retrieve mail using POP3 from a client, many options can be used such as Sun Microsystems Inc. 'S Mailtool, Qualcomm Inc.' S Eudora, Netscape Comm. Corp. 'S Netscape Mail and Microsoft Corp.' S Outlook Express.
POP3 is not intended to provide mail manipulation operations on the server extensively. On POP3, mail is taken from the server and then deleted (or may not be removed). Everything about the POP3 protocol is discussed in RFC (Request For Comment) 1725. Protocol is higher and more complex, that is IMAP4, is discussed in RFC 1730.
POP3 mode
There are two types of modes on the POP3 offline mode and inline mode. In the offline mode, POP3 mail retrieve and then delete the saved from the server. POP3 works fine in this mode, because it primarily was designed to act as a mail system that has the character of the "store-and-forward". Server, the offline mode, acting as a reservoir that holds the mail until the user requests it.
In the inline mode, will take mail from the POP3 server without deleting the mail that has been captured. This mode is preferred by users who often change places (nomadic user) because it allows them to see the same mail from a place or a different computer. However, for the nomadic user is always working and traveling always carry a notebook, and still wants his mail on the server are not deleted, of course, want to pick up mail every time the mail is not all that will be drawn, but only the mail that he had never just look at who will be taken. This user desires can be fulfilled by using the information on the client that allows to mark mail that has ever seen. Any client that supports POP3 service inline mode will store this information in a file. The users who use Netscape Mail, files that store this information is popstate.dat file, usually located in / Program Files / Netscape / Users / Mail. Mail the file to tell where it had taken so it does not need to be taken again. If the file is deleted then of course the decision-mail all mail will be drawn next. The contents of the file popstate.dat for a user who has logged such as 'Jim' on the POP3 server students.itb.ac.id are as follows:
# Netscape POP3 State File
# This is a generated file! Do not edit.
* Jim students.itb.ac.id
k c67ee091087ed814337b4cb31e0d488c
k 8541822a98e890b88d8299d034993f61
k 652e17a1c984e610e4e55257c07b6ff4
On this file the code behind the letter k is the unique-id. These unique-id uniquely identifies a mail in the maildrop so that each has a unique mail-id is different. If for example our mail in the local computer is deleted while we want to read it again, so before we take the maildrop from the server, file popstate.dat must be removed first. If we do not delete the file then there will be a message: "no new messages on server", which is given by the Netscape Mail. For Eudora users, files that store this information is lmos.dat file, whereas for Outlook Express users typically use pop3uidl.dat file.
Basic operation of POP3
At first, the server starts the POP3 service by listening to requests on TCP port 110. When a client requests the service, then there is a TCP connection to the server. At the time the relationship began, the POP3 server sends a greeting (opening words). After that the client will give the command (command) to the server and the POP3 server will give a response (answer) until the connection is closed or canceled. Keep in mind that the user does not enter this command, but the software of the client who sends this command to the server.
POP3 commands consist of a keyword is not case sensitive (capitalization does not question or not), which can be followed by one or more arguments. Keywords and arguments each separated by a SPACE character (space). Title consists of three or four characters, while each argument can be up to 40 characters. The answer in the POP3 consist of a status indicator and a keyword that can be followed by additional information. There are two status indicators: positive ("+ OK") and negative ("-ERR"). Server should provide the answer + OK and-ERR in capital letters. At a certain command, the server will give an answer that consists of several lines.
A POP3 session connection is built through three stages, namely stages of authorization, transaction and update. Once the TCP connection starts and the POP3 server has sent a greeting, then the relationship has entered a stage of the session authorization. At this stage the client sends the user name and password to the server for that user membuktian authenticity in order to retrieve his mail. When the client has managed to prove her identity, the server will obtain information relating to the mail client owned, and sessions are now entering the phase of the transaction. At this stage of a process of receiving mail, marking mail for deletion, cancellation marking for deletion, the appearance of the identity details of statistics mail or mail. By the time the client has quit command to end the relationship, then entered the stage of update sessions. At this stage the server will execute all orders obtained during the transaction and close the session and subsequent TCP connection is closed.
A server has to answer an unknown command, not implemented, or not in accordance with the syntax with a negative status indicator. The server also must provide a negative status indicator, if any client that provides commands that should not at this stage. There is no general method that can be used by the client to distinguish between the servers that do not implement the additional commands to the server that is unable or unwilling to process the additional orders.
A POP3 server may have autologout timer for client who is not active within a certain time frame. Timer like this should at least have a span of 10 minutes. If a server receives any command from the client within that time, then this is enough to reset the timer autologout. When the time span of the timer is up, with no activity from the client session does not enter the phase relationship UPDATE. Server will close the TCP connection without removing mail or send a reply to the client.
All messages are delivered during the session should be adjusted POP3 connection to the standard format of Internet text messages. Internet text messages this is discussed in detail in RFC 822. Table 1. below shows the commands in the following POP3 commands the stage where it is used.
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POP3 commands listed in the table above are the basic commands that are served by all POP3 server with minimal implementation. In addition to the above command is still there are a few additional commands that permit a POP3 client to be more free in his handling of mail at the POP3 server related. Additional command and its stage is justified to use these commands can be seen in Table 2. below:
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POP3 understand all the commands that are shown by the table above, but POP3 is only aware of three answers: "+ OK", "-ERR" and a list of answers to that end with "." (An indicator of the end of a list of answers). Keep in mind that except for the command STAT, LIST, and UIDL, the answer given by the POP3 server to any command is just a "+ OK" and "-ERR".
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