Introduction:
1. The POP is available for an email protocol for offline models of C / S structures, which has been developed to the third edition, called POP3. Offline models can not be operated online, unlike IMAP4 (Netscape support IMAP4)
2. When the client is connected to the server and query the new email, all the mail specified by the client will be downloaded to the client, after downloading, the email client can delete or modify any email No need to further interact with the email server.
3. POP3 customers send commands to the POP3 server and wait for a response, and the POP3 command uses the command line to reply with the ASCII code. The server response is composed of a separate command line, or a plurality of command lines, responding that the first line is in ASCII text OK or -RR, indicating that the corresponding operation status is successful or failed.
4. There are three states, accredited status, processing status, and update status in the POP3 protocol. When the client is connected to the server, once the client provides its own identity and successfully confirmed, that is, the client issues a Quit command after the corresponding operation is transferred, then the client issues a Quit command, then enter the update state, after the update is finally heavy State the state.
5. Command statement of the recognized state
In general, most of the existing POP3 clients performs a username and password using ASCII clear text. When the recognizable state is waiting for a customer connection, the customer issues a connection, and is sent by the command user / pass to send a plaintext username on the network. The password confirms to the server. Once the confirmation is successful, turn to the processing status. In order to avoid the issue of sending a clear text password, there is a new authentication method, the command is APOP, using the APOP, the password is encrypted before transfer. When the first time is connected to the server, the POP3 server sends an ASCII code greeting to the client. This greetings are unique to each client consisting of a string character. The client is related to the time, then the client puts its pure After the text password is attached to the string received from the server, then calculate the MD5 single-out function message summary of the result string, the client sends the user name with the MD5 message summary as the parameter of the APOP command. Currently, most Windows's mail client software does not support apop commands, QPopper support.
6. The POP3 command code is as follows:
Command Parameter Status Description ------------------------------------------ User UserName Approve this If the command and the following pass command will result in the status to convert the pass password approved apop name, Digest recognized Digest is MD5 message summary -------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- ------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- Valves, each identifier of the POP3 session will be unique list of lists to return the number of emails and the size of each message RETR [MSG #] process returns all text dele [msg #] processing by the message identified by the parameter. The server will mark the message from the parameter identity as delete, and the RSET NONE process server will reset all the mail that is marked as deleted, and the dele command TOP [MSG #] process server will return the first N line named by the parameter identifier Content, n must be positive integer NOOP NONE processing server to return a positive response --------------------------------- ------- Quit None update a. Client wants to end this session b. If the server is in 'processing' status, then the 'update' status will be removed to delete mail C. Mark C. resulting in processing status To the update state, return to the transformation of the recognized state. If this command is issued, the server is in the 'approval' state, then the session is ended, and the 'update' state is not performed.
7. The POP3 protocol waits for the customer connection request on the TCP / 110 port.
8. If the password is clear text, how do I listen?
The following command displays the process of displaying the POP3 connection and command on the screen after the server is run:
#sniffit -a -a. -p 110 -b -s 192.169.11.12note: 192.168.11.12 is the client IP address you need to install Sniffit port listeners in advance
9. Consider this situation, if the customer assumes 15 letter waiting to receive, but due to line problems, it is broken when the line problem is received, why is it starting from the first seal next time, That is why did the top 10 have not been removed from the server? Any mail deletion must perform a delete operation on the mail that is marked as deleted after the quit command is issued, due to the midway disconnection, still in the processing status, no chance will execute the Quit command for status conversion.
10. Pop3 session is locked by Another Session, please wait at the POP3 program internal mechanism to lock the session because abnormal operations cause the POP3 program internal mechanism.
11. The processing mechanism of Foxmail and OE (Outlook Express) is different. A. Assume that there are three emails on the server waiting for the client to receive. Different from Foxmail and OE lies in that Foxmail deletes an edge, while OE is all received, then fully marked as deleting final execution quit commands.
b. Foxmail's remote mail management is a very good management tool. It is assumed that there are three letters on the server. We don't want to receive it directly from the server; for the second seal, want to receive but do not delete, the third seal This time I don't want to receive, and the commands issued by Foxmail after the respective marks are
Dele 1Retr 2 quit
c. If there is no foxmail, there is a few big letters, I don't want to receive it, I want to delete it directly, or want to see who these two is sent? Use the command line to operate directly in the Windows DOS window, such as: # Telnet My.ISP.NET 110 User "Username" pass "password" list dele 3dele 5quit
