See also
- Transparent SMTP proxy
- SpamAssassin, popular open source spam filtering that uses razor and other techniques to detect spam.
- Qpsmtpd, a similar project
| Original author(s) | John Hanna |
|---|---|
| Developer(s) | Thomas Eckardt in association with the ASSP community |
| Stable release | 2.8.1(23131) / May 11, 2023 |
| Preview release | 2.8.2(23136) / May 16, 2023 |
| Written in | Perl |
| Operating system | Cross-platform |
| Type | Email spam filter |
| License | GNU General Public License |
| Website | assp.sourceforge.net |
The Anti-Spam SMTP Proxy (ASSP) is an open-source, Perl based, platform-independent transparent SMTP proxy server.
Some ASSP's features are:
A Domain Name System blocklist, Domain Name System-based blackhole list, Domain Name System blacklist (DNSBL) or real-time blackhole list (RBL) is a service for operation of mail servers to perform a check via a Domain Name System (DNS) query whether a sending host's IP address is blacklisted for email spam. Most mail server software can be configured to check such lists, typically rejecting or flagging messages from such sites.
A tarpit is a service on a computer system 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.
Various anti-spam techniques are used to prevent email spam.
Email spam, also referred to as junk email, spam mail, or simply spam, is unsolicited messages sent in bulk by email (spamming). The name comes from a Monty Python sketch in which the name of the canned pork product Spam is ubiquitous, unavoidable, and repetitive. Email spam has steadily grown since the early 1990s, and by 2014 was estimated to account for around 90% of total email traffic.
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.
A bounce message or just "bounce" is an automated message from an email system, informing the sender of a previous message that the message has not been delivered. The original message is said to have "bounced".
Email filtering is the processing of email to organize it according to specified criteria. The term can apply to the intervention of human intelligence, but most often refers to the automatic processing of messages at an SMTP server, possibly applying anti-spam techniques. Filtering can be applied to incoming emails as well as to outgoing ones.
Email authentication, or validation, is a collection of techniques aimed at providing verifiable information about the origin of email messages by validating the domain ownership of any message transfer agents (MTA) who participated in transferring and possibly modifying a message.
spamd is an ISC-licensed lightweight spam-deferral daemon written under the umbrella of the OpenBSD project. spamd works directly with smtp connections, and supports features such as greylisting, minimising false positives compared to a system that does full-body analysis. spamd is designed to work in conjunction with pf(4), and should be fully functional on any POSIX system where pf is available, i.e. OpenBSD, NetBSD, FreeBSD and DragonFly BSD.
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.
MIMEDefang is a GPL licensed framework for filtering e-mail. It uses sendmail's "Milter" API, some C glue code, and some Perl code to let the user write high-performance mail filters in Perl.
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.
MailChannels is a Canadian technology company specializing in email security and delivery solutions for businesses and internet service providers (ISPs). Founded in 2004 by Ken Simpson and headquartered in Vancouver, British Columbia. MailChannels has grown to become a trusted name in the email security and infrastructure market. The company offers a range of products and services aimed at protecting email systems from spam, phishing, and other malicious content, while also ensuring reliable email delivery for legitimate messages.
Backscatter is incorrectly automated bounce messages sent by mail servers, typically as a side effect of incoming spam.
Stockade is a TCP-layer blocking tool written in C++. It denies TCP/IP access to registered IP addresses by using the ipfw packet filter. It targets spam prevention, but may also be used against other attackers
Messaging Security is a program that provides protection for companies' messaging infrastructure. The programs includes IP reputation-based anti-spam, pattern-based anti-spam, administrator defined block/allow lists, mail antivirus, zero-hour malware detection and email intrusion prevention.
The following outline is provided as an overview of and topical guide to the Perl programming language:
People tend to be much less bothered by spam slipping through filters into their mail box, than having desired e-mail ("ham") blocked. Trying to balance false negatives vs false positives is critical for a successful anti-spam system. As servers are not able to block all spam there are some tools for individual users to help control over this balance.
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 and one or more content filters.
Haraka is an open source SMTP server. Its architecture is plugin-oriented and event-driven. The server and its plugins are written in JavaScript using the Node.js framework.