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POP3 Lock
This entry is compiled and applied to the scientific entry of "Science China" encyclopedia. POP3, full name is "Post Office Protocol-version 3", which is "Post Office Protocol version 3". is a member of the TCP/IP protocol family, defined by RFC1939. This agreement is primarily intended to support the use of clients to remotely administer e-Mail on the server. The POP3 protocol, which provides SSL encryption, is known as pop3s. The POP protocol supports "offline" mail processing. The process is that the message is sent to the server, and the e-mail client invokes the mail client program to connect to the server and downloads all unread e-mails. This offline access mode is a store-and-forward service that sends mail from the mail server to a personal terminal machine, typically a PC or MAC. Once the message is sent to a PC or Mac, the Mail on the mail server will be deleted. However, most of the current POP3 mail servers can "download mail only, server side does not delete", that is, the improved POP3 protocol.
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Chinese name
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Post Office Protocol version 3
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Foreign names
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Post Office protocol-version 3
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Abbreviation
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POP3
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Defined by
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RFC1939 definition
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Support
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Clients manage e-mail remotely
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Role
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download messages only, server side does not delete
Directory
- 1 protocol properties
- 2 principle
- ? applicable range
- ? pop protocol
- ? command response
- ? three different states
- ? Command Statements
- ? POP3 Command Code
- ? wait
- ? Monitor
- ? Interrupts
- ? Lock
- ? processing mechanism
- 3 Operation Guide
- 4 FAQs
Protocol feature POP3 Protocol default port: 110POP3 protocol Default transport protocol: The architecture structure that the TCPPOP3 protocol applies to: the access mode of the C/SPOP3 protocol: offline access the POP3 protocol is shown in the schematic.POP3 ProtocolThe application of the principle pop is applicable to the offline model of C/s structure e-mail protocol, has now developedPOP3To the third edition, called POP3. The offline model cannot be operated online, and pop does not support extended operations on server mail, which requires a more advanced IMAP4 protocol to complete. The POP protocol supports the use of ASCII code to transmit data messages, which can either be instructions or be answered. The POP protocol protocol supports offline mail processing, and when a message is sent to the server, the e-mail client invokes the mail client program. Download all unread e-mails (this offline access mode is a storage and forwarding service). When a message is sent from the mail server to a personal computer, the mail server deletes the message (but many POP3 servers now support "Download mail, server does not delete mail" This means that the POP protocol is improved in POP3). Command response POP3 the client sends commands to the POP3 server and waits for a response, the POP3 command takes the form of a command line and is represented by an ASCII code. The server response is made up of a separate command line or multiple command lines that respond to the first line in ASCII text +ok or-err (OK refers to success,-ERR refers to failure) to indicate whether the corresponding operation state succeeded or failed. Three status authentication status, processing status and update status. When the client establishes a connection with the server, the client sends its own identity to the server (in this case, the account and password) and is successfully confirmed by the server, that is, the client is transferred from the approved state to the processing state, and the client issues a quit command after completing the corresponding operation, such as the list of unread messages, and exits the processing status The connection to the server is disconnected after you start to download unread messages to the computer locally after you finally return to the authentication status confirmation. Specific principles such as waiting for connection authentication quit Command c--| Certification | ————— | processing | —————— | update |----s|__________________________________| re-entry certification status. Command statement currently most POP client and server are using ASCII code to send the user name and password in plaintext, in the authentication state when the server waits for the client connection, the client makes connection request, and the User/pass user identity information data composed by the command is sent to the server. After the server confirms the client identity, the connection status is transferred from the authentication state to the processing state, in order to avoid the security issue of sending plaintext password, there is a new and more secure authentication method, named Apop, using APOP, password is encrypted before transmission, when the client and the server first establish the connection, The POP3 server sends an ASCII text greeting to the client, which consists of a string of characters that are unique to each client, usually local time. The client then appends its plaintext password to the string that was just accepted, then computes the message data of the new string's MD5 single-out function value, and the client then encrypts the user name and MD5 messageThe summary is sent to the server as a parameter of the APOP command. However, most mail clients on Windows currently do not support the APOP protocol. Qpopper support. POP3 Command Code
| Command |
Describe |
| USER [Username] |
Process User Name |
| PASS [Password] |
Handling User passwords |
| APOP [Name,digest] |
Recognition Digest is a MD5 message digest |
| STAT |
Processing the request server sends back statistics about the mailbox, such as the total number of messages and the total number of bytes |
| UIDL [msg#] |
Handles the unique identifier of the returned message, and each identifier for the POP3 session will be unique |
| LIST [msg#] |
Process the number of returned messages and the size of each message |
| RETR [msg#] |
Handles all text that returns the message identified by the parameter |
| DELE [msg#] |
The processing server marks the message identified by the parameter as deleted and executed by the QUIT command |
| RSET |
The processing server resets all messages marked for deletion to undo the dele command |
| TOP [msg# N] |
The processing server returns the first n rows of the message identified by the parameter, and n must be a positive integer |
| NOOP |
The processing server returns a positive response |
| QUIT |
Terminating a session |
A. The client wants to end this session B. If the server is in the ' processing ' state, it will go to the ' Update ' state to remove any messages marked for deletion c. Transitions that result from processing state to update status and return to approved status D. If the server is in an ' approved ' state when this command is issued, end the session without ' Update ' status. Wait for the POP3 protocol to wait for a client connection request on the tcp/110 port. [1] Listening if the password is clear, how can I listen?POP3The following command displays the POP3 connection and the command sending process on the screen after the server is run: #sniffit-a-a.-p110-b-s192.169.11.12note : 192.168.11.12 is the client IP address you need to install Sniffit this port listener interrupt to consider this situation, if the customer in the receipt of mail, assuming that 15 letters waiting to receive, but because of the line problem, received the 10th letter was disconnected, why the next time to collect still from the first letter, Which is why the first 10 were not removed from the server? Any deletion of a message must be deleted after the QUIT command has been issued, and is still in a processing state due to a broken line, and there is no opportunity to execute the QUIT command for state transitions. Lock POP3 Session is locked by another session,please wait for minutes then try again. Due to abnormal operation, the internal mechanism of the POP3 program locks the session. The processing mechanism differs from the foxmail of OE (outlookexpress). A. Assume that there are three messages on the server waiting for the client to receive. The difference between the foxmail and OE is that foxmail deletes one per mark, and OE waits for all of them to be removed and then all marked for deletion and the last execution of the QUIT command. Foxmailoe-------------------------------RETR1RETR1POP3DELE1RETR2RETR2RETR3DELE2DELE1RETR3DELE2DELE3DELE3QUITQUITB. Foxmail Remote Mail Management is a very good management tool, assuming that there are three letters on the server, on the first, we do not want to receive from the server to delete; On the second, want to receive but do not delete, on the third, this time do not want to receive, The command issued by the last Foxmail after marking is DELE1RETR2QUITC. If there is no foxmail, just a few big letters blocked, I do not want to receive, want to delete it directly, or want to see the two who sent it? Use the command line directly under Windows DOS window, such as: # telnetmyispnet110userusernamepasspasswordlistdele3dele5quit--Operation Guide Server allows compliance with POP3 (Postofficeprotocol,version3 Mail Delivery protocol , version 3) of the mail client connects to the IMAIL server. These mail client software includes Outlookexpress,outlook,netscapemessenger or Communicator,eudora,pegasus,nupop,z-mail,foxmail,thebat, Kmail, and Unixmail[2]. POP3 clients usually use "off-line" to access the mail server offline, periodically access the mail server, download the mail to the customer's computer, and then disconnect from the server. Typically, messages are temporarily stored on the server, and when the client downloads the messages, they are deleted by the server and are no longer retained. This is a very good way for users who are always reading messages on the same computer. Another way, called "online", is that the mail client always stays connected to the server. The message is kept on the server, the client does not download the message to the client computer, and the user can read the messages that remain on the server online. Users who often use different computers are suited to this approach. The ImailPOP3 service can act as a Windows NT service, completely hidden or run in a way that has some interaction. The service will always run even if you log out of the system.POP3 operation DiagramIMail also provides another way to access IMAP4 (INTERNETMESSAGEACCESSPROTOCOLVERSION4). The IMAP4 service provides both "online" and "Offline" access. Logging on login defaults, the POP3 service uses the system account to log into the system. You can change this login method: Pop3[3] 1, in the Control Panel, start the Services applet. 2. Select the IMAILPOP3 Server service and click Startup. 3. (optional) Select the Startuptype you want. 4, in LogonAs, select the correct login account: Imailserversystemaccount. If you have a mail host that uses the WindowsNT user database as the IMAIL user database, you need to use that account. Allowservicetointeractwithdesktop. With this account, when any user log in to the system, there will be a imail icon on the desktop. Thisaccount. In this way, if your host does not use the WindowsNT user database, you can enter the user account you wish, and confirm that the account is a host administrator. If you have a mail host that uses an external database, confirm that the account can access the external database. Configuringthe POP3 Server configures the POP3 server to configure the POP3 server: 1. In imailadministrator, select "localhost" in the left panel. 2. Select the "Services" directory and click on the POP3.POP3 panel to appear. 3. Enter the options described below to configure the POP3 service. 4. Click the button apply to save the settings. 5. Stop the service, wait 5-10 seconds, and then restart the service. When you click the button Stop/start, the settings change automatically. FAQ 1. What is POP3? A: POP3 is the abbreviation for post Office Protocol-version 3, the Post Office Protocol version 3, which is a protocol for reading messages from a mail server. Used to transfer messages from the POP server to the user agent. The user agent responsible for receiving mail is called a pop customer, and the server responsible for sending the message is called the POP server. 2. Why do I need POP3? A: Through the POP3 protocol, the recipient does not need to participate in the mail to the mail server reading process, Simplifies user operations. The recipient can "offline" mail processing, very convenient to receive, read mail. 3. What are pop commands and answers? A: Pop customers use the pop command to send a request to a POP server, such as a pass commandTransfer account password, RETR command request to send message content, etc. the POP server responds with this response, "+ok" means the command succeeds, "-err" means the command fails, followed by a simple text description, such as "+ok Password required for Bob" Indicates that the user command executes successfully and requires the customer to enter a password for authentication. 4. What are the status of the POP3 protocol? A: There are three states of POP3: AUTHORIZATION (Authorization), TRANSACTION (processing), update (updated). When TCP is established, POP3 enters the "authorization" state, and the customer needs to use the user/ Pass for authentication. After verification, POP3 into the "processing" status, customers can send list,retr and other commands to query, get mail. When the customer sends the "Update" command in this state, POP3 enters the "updated" state, and the server finishes processing the command and returns to the "Authorization" state. 5. When the server receives the DELE command sent by the customer, is the message removed from the server immediately? A: After the server receives the DELE command, Simply mark the message as deleted, and the actual delete operation is performed in the updated state. If the update status has not yet been reached, the customer can send the RSet command to undo the previous Dele command. 6. POP3 in the user's password is clear-text transmission, with security implications, what should I do? A: POP3 uses the pass command to transfer the user's password and send it in clear text, thus having a security risk. Now, POP3 provides another command apop, can safely transfer user password, avoid security hidden trouble.more Atlas of the term bookEntry picture(6)
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Resources
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- 1. POP3 Protocol Command Source code and working principle . Protocol analysis Network [citation date 2012-10-19]
- 2. POP3 settings and application of common mailbox
- 3. POP3 Operation guide and common mail collection software settings
POP3, full name "Post Office Protocol-version 3", or "Post Office Protocol version 3"
