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Transparent SMTP Proxy
SMTP proxies are specialized mail transfer agents (MTAs) that, similar to other types of proxy servers, pass SMTP sessions through to other MTAs without using the store-and-forward approach of a typical MTA. When an SMTP proxy receives a connection, it initiates another SMTP session to a destination MTA. Any errors or status information from the destination MTA will be passed back to the sending MTA through the proxy. Uses SMTP proxies are commonly used to process and filter inbound and outbound email traffic. Inbound SMTP proxying SMTP proxies often serve as the initial, network-facing layer in an email system, processing SMTP connections from clients before forwarding data to a second layer of mail servers. SMTP proxies often implement the first and/or only layer of defence in an inbound anti-spam filtering system, where they can analyze messages using a spam content filter or antivirus program, block or rate limit connections using DNS blacklists and reputation systems, an ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Mail Transfer Agent
The mail or post is a system for physically transporting postcards, letters, and parcels. A postal service can be private or public, though many governments place restrictions on private systems. Since the mid-19th century, national postal systems have generally been established as a government monopoly, with a fee on the article prepaid. Proof of payment is usually in the form of an adhesive postage stamp, but a postage meter is also used for bulk mailing. With the advent of email, the retronym "snail mail" was coined. Postal authorities often have functions aside from transporting letters. In some countries, a postal, telegraph and telephone (PTT) service oversees the postal system, in addition to telephone and telegraph systems. Some countries' postal systems allow for savings accounts and handle applications for passports. The Universal Postal Union (UPU), established in 1874, includes 192 member countries and sets the rules for international mail exchanges as a Specialize ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Tarpit (networking)
A tarpit is a service on a computer system (usually a server) that purposely delays incoming connections. The technique was developed as a defense against a computer worm, and the idea is that network abuses such as spamming or broad scanning are less effective, and therefore less attractive, if they take too long. The concept is analogous with a tar pit, in which animals can get bogged down and slowly sink under the surface, like in a swamp. The original tarpit idea Tom Liston developed the original tarpitting program ''LaBrea''. It can protect an entire network with a tarpit run on a single machine. The machine listens for Address Resolution Protocol requests that go unanswered (indicating unused addresses), then replies to those requests, receives the initial SYN packet of the scanner and sends a SYN/ACK in response. It does not open a socket or prepare a connection, in fact it can forget all about the connection after sending the SYN/ACK. However, the remote site sends ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Synchronization (computer Science)
In computer science, synchronization refers to one of two distinct but related concepts: synchronization of processes, and synchronization of data. ''Process synchronization'' refers to the idea that multiple processes are to join up or handshake at a certain point, in order to reach an agreement or commit to a certain sequence of action. ''Data synchronization'' refers to the idea of keeping multiple copies of a dataset in coherence with one another, or to maintain data integrity. Process synchronization primitives are commonly used to implement data synchronization. The need for synchronization The need for synchronization does not arise merely in multi-processor systems but for any kind of concurrent processes; even in single processor systems. Mentioned below are some of the main needs for synchronization: '' Forks and Joins:'' When a job arrives at a fork point, it is split into N sub-jobs which are then serviced by n tasks. After being serviced, each sub-job waits until al ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
DomainKeys Identified Mail
DomainKeys Identified Mail (DKIM) is an email authentication method designed to detect forged sender addresses in email (email spoofing), a technique often used in phishing and email spam. DKIM allows the receiver to check that an email claimed to have come from a specific domain was indeed authorized by the owner of that domain. It achieves this by affixing a digital signature, linked to a domain name, to each outgoing email message. The recipient system can verify this by looking up the sender's public key published in the DNS. A valid signature also guarantees that some parts of the email (possibly including attachments) have not been modified since the signature was affixed. Usually, DKIM signatures are not visible to end-users, and are affixed or verified by the infrastructure rather than the message's authors and recipients. DKIM is an Internet Standard. It is defined in RFC 6376, dated September 2011; with updates in RFC 8301 and RFC 8463. Overview The need for e ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Spam (electronic)
Spamming is the use of messaging systems to send multiple unsolicited messages (spam) to large numbers of recipients for the purpose of commercial advertising, for the purpose of non-commercial proselytizing, for any prohibited purpose (especially the fraudulent purpose of phishing), or simply repeatedly sending the same message to the same user. While the most widely recognized form of spam is email spam, the term is applied to similar abuses in other media: instant messaging spam, Usenet newsgroup spam, Web search engine spam, spam in blogs, wiki spam, online classified ads spam, mobile phone messaging spam, Internet forum spam, junk fax transmissions, social spam, spam mobile apps, television advertising and file sharing spam. It is named after Spam, a luncheon meat, by way of a Monty Python sketch about a restaurant that has Spam in almost every dish in which Vikings annoyingly sing "Spam" repeatedly. Spamming remains economically viable because advertisers have no ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Email Server
Within the Internet email system, a message transfer agent (MTA), or mail transfer agent, or mail relay is software that transfers electronic mail messages from one computer to another using SMTP. The terms mail server, mail exchanger, and MX host are also used in some contexts. Messages exchanged across networks are passed between mail servers, including any attached data files (such as images, multimedia or documents). These servers also often keep mailboxes for email. Access to this email by end users is typically either via webmail or an email client. Operation A message transfer agent receives mail from either another MTA, a mail submission agent (MSA), or a mail user agent (MUA). The transmission details are specified by the Simple Mail Transfer Protocol (SMTP). When a recipient mailbox of a message is not hosted locally, the message is relayed, that is, forwarded to another MTA. Every time an MTA receives an email message, it adds a trace header field to the top of the he ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Store And Forward
Store and forward is a telecommunications technique in which information is sent to an intermediate station where it is kept and sent at a later time to the final destination or to another intermediate station. The intermediate station, or node in a networking context, verifies the integrity of the message before forwarding it. In general, this technique is used in networks with intermittent connectivity, especially in the wilderness or environments requiring high mobility. It may also be preferable in situations when there are long delays in transmission and variable and high error rates, or if a direct, end-to-end connection is not available. Modern store and forward networking * Store and forward originates with delay-tolerant networks. No real-time services are available for these kinds of networks. * Logistical Networking is a scalable form of store and forward networking that exposes network-embedded buffers on intermediate nodes and allows flexible creation of services ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Libevent
libevent is a software library that provides asynchronous event notification. The libevent API provides a mechanism to execute a callback function when a specific event occurs on a file descriptor or after a timeout has been reached. libevent also supports callbacks triggered by signals and regular timeouts. libevent is meant to replace the event loop found in event-driven network servers. An application can just call event_dispatch() and then add or remove events dynamically without having to change the event loop. Currently, libevent supports /dev/poll, kqueue(2), POSIX select(2), Windows IOCP, poll(2), epoll(7) and Solaris event ports. It also has experimental support for real-time signals. The exposed event API is uniform over all of the supported platforms. As a result, libevent allows for portable application development and provides "the most scalable event notification mechanism available on an operating system". Using callbacks on signals, libevent makes it possibl ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Netty (software)
Netty is a non-blocking I/O client-server framework for the development of Java network applications such as protocol servers and clients. The asynchronous event-driven network application framework and tools are used to simplify network programming such as TCP and UDP socket servers. Netty includes an implementation of the reactor pattern of programming. Originally developed by JBoss, Netty is now developed and maintained by the Netty Project Community. Besides being an asynchronous network application framework, Netty also includes built-in implementations of SSL/ TLS, HTTP, HTTP/2, HTTP/3, WebSockets, DNS, Protocol Buffers, SPDY and other protocols. Netty is not a Java web container, but is able to run inside one, and supports message compression. Netty has been actively developed since 2004. Beginning with version 4.0.0, Netty also supports the usage of NIO.2 as a backend, along with NIO and blocking Java sockets. See also * Application server * Node.js * Twisted (so ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Node
In general, a node is a localized swelling (a "knot") or a point of intersection (a vertex). Node may refer to: In mathematics *Vertex (graph theory), a vertex in a mathematical graph *Vertex (geometry), a point where two or more curves, lines, or edges meet. *Node (autonomous system), behaviour for an ordinary differential equation near a critical point *Singular point of an algebraic variety, a type of singular point of a curve In science and engineering Astronomy *Orbital node, the points where an orbit crosses a plane of reference ** Lunar node, where the orbits of the sun and moon intersect ** Longitude of the ascending node, how orbital nodes are parameterized Biology *Lymph node, an immune system organ used to store white blood cells *Node of Ranvier, periodic gaps in the insulating myelin sheaths of myelinated axons *Sinoatrial node and atrioventricular node, specialized tissues in the heart responsible for initiating and coordinating the heartbeat *Primitive knot or p ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Nginx
Nginx (pronounced "engine x" ) is a web server that can also be used as a reverse proxy, load balancer, mail proxy and HTTP cache. The software was created by Igor Sysoev and publicly released in 2004. Nginx is free and open-source software, released under the terms of the 2-clause BSD license. A large fraction of web servers use Nginx, often as a load balancer. A company of the same name was founded in 2011 to provide support and ''Nginx Plus'' paid software. In March 2019, the company was acquired by F5, Inc. for $670 million. Popularity W3Tech's web server count of all web sites ranked Nginx first with 33.6%. Apache was second at 31.4% and Cloudflare Server third at 21.6%. , Netcraft estimated that Nginx served 22.01% of the million busiest websites with Apache a little ahead at 23.04%. Cloudflare at 19.53% and Microsoft Internet Information Services at 5.78% rounded out the top four servers for the busiest websites. Some of Netcraft's other statistics show Ngi ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Asynchronous I/O
In computer science, asynchronous I/O (also non-sequential I/O) is a form of input/output processing that permits other processing to continue before the transmission has finished. A name used for asynchronous I/O in the Windows API is overlapped I/O. Input and output (I/O) operations on a computer can be extremely slow compared to the processing of data. An I/O device can incorporate mechanical devices that must physically move, such as a hard drive seeking a track to read or write; this is often orders of magnitude slower than the switching of electric current. For example, during a disk operation that takes ten milliseconds to perform, a processor that is clocked at one gigahertz could have performed ten million instruction-processing cycles. A simple approach to I/O would be to start the access and then wait for it to complete. But such an approach (called synchronous I/O, or blocking I/O) would block the progress of a program while the communication is in progress, leaving ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
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