NNTP is a protocol for publishing online news mails to NNTP servers or NNTP clients (news readers) on the Internet, providing reliable stream-based news transmission through the Internet, and providing news distribution, query, retrieval and transmission. NNTP also specially designed to save news articles on the server in the central database, so that users can select specific items to read, and also provided indexing, cross-reference and termination of expired news.
NNTP uses TCP port number 1 19.
MAPI stands for message application programming interface. Mail or mail composition application interface. An open and comprehensive email writing interface for programmers to create email writing and workgroup applications (such as email, planning, scheduling and document management). In the distributed client/server environment, MAPI provides enterprise mail composition service within the scope of WINDOWS Open Service System (WOSA). Windows applications can connect to all kinds of messaging systems, from Micorsoft Mail to Novell MHS. However, MAPI is limited to the daily work level, that is, mail-aware application, which can exchange mail and data on the network.
Imap4 (Internet Message Access Protocol 4) is the fourth version of Internet information access protocol, which is a standard protocol for accessing e-mail from remote servers. It is a client/server model protocol, and the server is responsible for receiving and saving users' emails. Users can decide whether to download this letter by browsing the letterhead. Users can also create or change folders or mailboxes on the server, delete letters or retrieve specific parts of letters.
Although both POP and IMAP handle incoming mail, their mechanisms are different. When users access e-mail, IMAP4 needs to access the server continuously. POP3 saves letters on the server. When the user reads the letter, all the contents will be downloaded to the user's computer immediately. Therefore, the server using IMAP4 protocol can be regarded as a remote file server, while the server using POP protocol can be regarded as a store-and-forward server. As far as the current application is concerned, the application of POP3 is far more extensive than that of IMAP4.
POP3 (post office protocol 3) POP is suitable for offline e-mail protocol with C/S structure.
At present, it has developed to the third edition, called POP3. It specifies how to connect a personal computer to Internet mail.
Server and electronic protocol for downloading e-mail. It is the first offline protocol standard for Internet e-mail,
POP3 allows users to store messages from a server to a local host (that is, their own computer) and delete them at the same time.
Mail is stored in a mail server, and the POP3 server is a mail receiving server following the POP3 protocol.
Used to receive e-mail.
POP is suitable for offline mode of C/S structure. Offline mode cannot be operated online, unlike IMAP4 (Netscape
Support IMAP4) When the client connects to the server and queries for new e-mail, all files specified by the client.
All emails to be downloaded will be downloaded to the client by the program. After downloading, the email client can delete or.
You can modify any message without further interaction with the email server. The POP3 client sends it to the POP3 server.
Command and wait for a response. POP3 command takes the form of command line and is expressed in ASCII code.
The server response consists of one or more command lines, and the first line of the response is ASCII code.
The text +OK or -ERR indicates whether the corresponding operation status is successful or failed. There are three states in the POP3 protocol.
Available status, processing status and update status.
When the client establishes contact with the server, once the client provides its own identity and successfully confirms it, it will be recognized.
The state transition to that processing state,
When the client issues a quit command after completing the corresponding operation, it enters the update state, and finally returns to recognition after the update.
Can be in the state.
SMTP: simple mail transfer protocol
(SMTP: Simple Mail Transfer Protocol)
SMTP is a protocol that provides reliable and efficient e-mail transmission. SMTP is a mail service based on FTP file transfer service, which is mainly used to transfer mail information between systems and provide notifications related to letters.
SMTP is independent of specific transmission subsystem, and only needs reliable and orderly data flow channel support. An important feature of SMTP is that it can transmit mail across networks, that is, "SMTP mail relay". Generally speaking, a network can be composed of TCP-accessible hosts on public networks, TCP-accessible hosts on TCP/IP networks separated by firewalls, and hosts using non-TCP transport layer protocols on other LANs/WANs. Using SMTP, mail transmission between processors on the same network can be realized, and mail transmission between a processor and other networks can also be realized through repeaters or gateways.
In this way, mail can be sent through a large number of intermediate repeaters or gateway hosts on the path from the sender to the receiver. The mail exchange server of Domain Name Service System (DNS) can be used to identify the next-hop IP address for transmitting mail.
Use port 25 during file transfer.