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Policyd-weight
policyd-weight is a mail filter for the Postfix mail transfer agent (MTA) written in Perl. It allows postfix to evaluate mail envelope information and to score mail against several DNS-based Blackhole Lists (DNSBL) before the mail is queued. The final score will determine whether a mail is rejected or accepted, in which case it is usually then subject to more resource intensive checks by a virus scanner and spam filter. Features policyd-weight works as a policy daemon in Postfix. It uses DNSBL, RHSBL, MX and A DNS queries of the envelope sender and HELO SMTP arguments to evaluate the possibility of either forgery or spam. Rejection happens based on an overall score, so a single blacklist entry may not cause the mail to be rejected. The score is determined by various checks and is not linear. The administrator is able to adjust scores for each check to meet her requirements. policyd-weight caches the most frequent queries to minimize bandwidth and CPU usage. The benefit of ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Anti-spam
Various anti-spam techniques are used to prevent email spam (unsolicited bulk email). No technique is a complete solution to the spam problem, and each has trade-offs between incorrectly rejecting legitimate email (false positives) as opposed to not rejecting all spam email (false negatives) – and the associated costs in time, effort, and cost of wrongfully obstructing good mail. Anti-spam techniques can be broken into four broad categories: those that require actions by individuals, those that can be automated by email administrators, those that can be automated by email senders and those employed by researchers and law enforcement officials. End-user techniques There are a number of techniques that individuals can use to restrict the availability of their email addresses, with the goal of reducing their chance of receiving spam. Discretion Sharing an email address only among a limited group of correspondents is one way to limit the chance that the address will be "harveste ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Spam Filtering
Various anti-spam techniques are used to prevent email spam (unsolicited bulk email). No technique is a complete solution to the spam problem, and each has trade-offs between incorrectly rejecting legitimate email (false positives) as opposed to not rejecting all spam email (false negatives) – and the associated costs in time, effort, and cost of wrongfully obstructing good mail. Anti-spam techniques can be broken into four broad categories: those that require actions by individuals, those that can be automated by email administrators, those that can be automated by email senders and those employed by researchers and law enforcement officials. End-user techniques There are a number of techniques that individuals can use to restrict the availability of their email addresses, with the goal of reducing their chance of receiving spam. Discretion Sharing an email address only among a limited group of correspondents is one way to limit the chance that the address will be "harvest ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Message Forgery
In cryptography, message forgery is sending a message so to deceive the recipient about the actual sender's identity. A common example is sending a spam or prank e-mail as if it were originated from an address other than the one which was really used. See also * Authentication * Message authentication code * Stream cipher attack Stream ciphers, where plaintext bits are combined with a cipher bit stream by an exclusive-or operation ( xor), can be very secure if used properly. However, they are vulnerable to attacks if certain precautions are not followed: *keys must neve ... {{crypto-stub Cryptographic attacks Practical jokes ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
GNU General Public License
The GNU General Public License (GNU GPL or simply GPL) is a series of widely used free software licenses that guarantee end users the Four Freedoms (Free software), four freedoms to run, study, share, and modify the software. The license was the first copyleft for general use and was originally written by the founder of the Free Software Foundation (FSF), Richard Stallman, for the GNU Project. The license grants the recipients of a computer program the rights of the Free Software Definition. These GPL series are all copyleft licenses, which means that any derivative work must be distributed under the same or equivalent license terms. It is more restrictive than the GNU Lesser General Public License, Lesser General Public License and even further distinct from the more widely used permissive software licenses BSD licenses, BSD, MIT License, MIT, and Apache License, Apache. Historically, the GPL license family has been one of the most popular software licenses in the free and open ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Free Software
Free software or libre software is computer software distributed under terms that allow users to run the software for any purpose as well as to study, change, and distribute it and any adapted versions. Free software is a matter of liberty, not price; all users are legally free to do what they want with their copies of a free software (including profiting from them) regardless of how much is paid to obtain the program.Selling Free Software (gnu.org) Computer programs are deemed "free" if they give end-users (not just the developer) ultimate control over the software and, subsequently, over their devices. The right to study and modify a computer program entails that |
Sender Policy Framework
Sender Policy Framework (SPF) is an email authentication method designed to detect forging sender addresses during the delivery of the email. SPF alone, though, is limited to detecting a forged sender claim in the envelope of the email, which is used when the mail gets bounced. Only in combination with DMARC can it be used to detect the forging of the visible sender in emails (email spoofing), a technique often used in phishing and email spam. SPF allows the receiving mail server to check during mail delivery that a mail claiming to come from a specific domain is submitted by an IP address authorized by that domain's administrators. The list of authorized sending hosts and IP addresses for a domain is published in the DNS records for that domain. Sender Policy Framework is defined in RFC 7208 dated April 2014 as a "proposed standard". History The first public mention of the concept was in 2000 but went mostly unnoticed. No mention was made of the concept again until a first att ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Type I And Type II Errors
In statistical hypothesis testing, a type I error is the mistaken rejection of an actually true null hypothesis (also known as a "false positive" finding or conclusion; example: "an innocent person is convicted"), while a type II error is the failure to reject a null hypothesis that is actually false (also known as a "false negative" finding or conclusion; example: "a guilty person is not convicted"). Much of statistical theory revolves around the minimization of one or both of these errors, though the complete elimination of either is a statistical impossibility if the outcome is not determined by a known, observable causal process. By selecting a low threshold (cut-off) value and modifying the alpha (α) level, the quality of the hypothesis test can be increased. The knowledge of type I errors and type II errors is widely used in medical science, biometrics and computer science. Intuitively, type I errors can be thought of as errors of ''commission'', i.e. the researcher unluck ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Greylisting (email)
Greylisting is a method of defending e-mail users against spam. A mail transfer agent (MTA) using greylisting will "temporarily reject" any email from a sender it does not recognize. If the mail is legitimate, the originating server will try again after a delay, and if sufficient time has elapsed, the email will be accepted. How it works A server employing greylisting temporarily rejects email from unknown or suspicious sources by sending 4xx reply codes ("please call back later"), as defined in the Simple Mail Transfer Protocol (SMTP). Fully capable SMTP implementations are expected to maintain queues for retrying message transmissions in such cases, and so while legitimate mail may be delayed, it should still get through. The temporary rejection can be issued at different stages of the SMTP dialogue, allowing an implementation to store more or less data about the incoming message. The trade-off is more work and bandwidth for more exact matching of retries with original messages. ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Amavis
Amavis is an open-source content filter for electronic mail, implementing mail message transfer, decoding, some processing and checking, and interfacing with external content filters to provide protection against spam and viruses and other malware. It can be considered an interface between a mailer ( MTA, Mail Transfer Agent) and one or more content filters. ''Amavis'' can be used to: * detect viruses, spam, banned content types or syntax errors in mail messages * block, tag, redirect (using sub-addressing), or forward mail depending on its content, origin or size * quarantine (and release), or archive mail messages to files, to mailboxes, or to a relational database * sanitize passed messages using an external sanitizer * generate DKIM signatures * verify DKIM signatures and provide DKIM-based whitelisting Notable features: * provides SNMP statistics and status monitoring using an extensive MIB with more than 300 variables * provides structured event log in JSON format * IPv6 ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
SpamAssassin
Apache SpamAssassin is a computer program used for anti-spam techniques, e-mail spam filtering. It uses a variety of spam-detection techniques, including Domain Name System, DNS and fuzzy checksum techniques, Bayesian spam filtering, Bayesian filtering, external programs, blacklists and online databases. It is released under the Apache License, Apache License 2.0 and is a part of the Apache Foundation since 2004. The program can be integrated with the Mail transfer agent, mail server to automatically filter all mail for a site. It can also be run by individual users on their own mailbox and integrates with several mail user agent, mail programs. Apache SpamAssassin is highly configurable; if used as a system-wide filter it can still be configured to support per-user preferences. History Apache SpamAssassin was created by Justin Mason, who had maintained a number of patches against an earlier program named ''filter.plx'' by Mark Jeftovic, which in turn was begun in August 1997. Mas ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Postfix (software)
Postfix is a free and open-source mail transfer agent (MTA) that routes and delivers electronic mail. It is released under the IBM Public License 1.0 which is a free software license. Alternatively, starting with version 3.2.5, it is available under the Eclipse Public License 2.0 at the user's option. Originally written in 1997 by Wietse Venema at the IBM Thomas J. Watson Research Center in New York, and first released in December 1998, Postfix continues to be actively developed by its creator and other contributors. The software is also known by its former names VMailer and IBM Secure Mailer. The name Postfix is a compound of "post" (which is another word for "mail") and "fix "(which is for other software that inspired Postfix development). In a study published on June 1, 2022 by E-Soft, Inc., approximately 34% of the publicly reachable mail-servers on the Internet ran Postfix, making it the second most popular mail server behind Exim. Note: this survey covers less than 25% ... [...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] |
