Electronic mail is a method of exchanging messages ("mail") between people using electronic devices. Email was thus conceived as the electronic (digital) version of, or counterpart to, mail, at a time when "mail" meant only physical mail. Email later became a ubiquitous communication medium, to the point that in current use, an email address is often treated as a basic and necessary part of many processes in business, commerce, government, education, entertainment, and other spheres of daily life in most countries.
An open mail relay is a Simple Mail Transfer Protocol (SMTP) server configured in such a way that it allows anyone on the Internet to send e-mail through it, not just mail destined to or originating from known users. This used to be the default configuration in many mail servers; indeed, it was the way the Internet was initially set up, but open mail relays have become unpopular because of their exploitation by spammers and worms. Many relays were closed, or were placed on blacklists by other servers.
The Spam Prevention Early Warning System (SPEWS) was an anonymous service that maintained a list of IP address ranges belonging to internet service providers (ISPs) that host spammers and show little action to prevent their abuse of other networks' resources. It could be used by Internet sites as an additional source of information about the senders of unsolicited bulk email, better known as spam.
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 whitelist, allowlist, or passlist is a mechanism which explicitly allows some identified entities to access a particular privilege, service, mobility, or recognition i.e. it is a list of things allowed when everything is denied by default. It is the opposite of a blacklist, which is a list of things denied when everything is allowed by default.
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".
The Spamhaus Project is an international organisation based in the Principality of Andorra, founded in 1998 by Steve Linford to track email spammers and spam-related activity. The name spamhaus, a pseudo-German expression, was coined by Linford to refer to an internet service provider, or other firm, which spams or knowingly provides service to spammers.
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.
A message submission agent (MSA), or mail submission agent, is a computer program or software agent that receives electronic mail messages from a mail user agent (MUA) and cooperates with a mail transfer agent (MTA) for delivery of the mail. It uses ESMTP, a variant of the Simple Mail Transfer Protocol (SMTP), as specified in RFC 6409.
Disposable email addressing, also known as DEA or dark mail or "masked" email, refers to an approach which involves a unique email address being used for every contact, entity, or for a limited number of times or uses. The benefit is that if anyone compromises the address or utilizes it in connection with email abuse, the address owner can easily cancel it without affecting any of their other contacts.
SpamCop is an email spam reporting service, allowing recipients of unsolicited bulk or commercial email to report IP addresses found by SpamCop's analysis to be senders of the spam to the abuse reporting addresses of those IP addresses. SpamCop uses these reports to compile a list of computers sending spam called the "SpamCop Blocking List" or "SpamCop Blacklist" (SCBL).
HTML email is the use of a subset of HTML to provide formatting and semantic markup capabilities in email that are not available with plain text: Text can be linked without displaying a URL, or breaking long URLs into multiple pieces. Text is wrapped to fit the width of the viewing window, rather than uniformly breaking each line at 78 characters. It allows in-line inclusion of images, tables, as well as diagrams or mathematical formulae as images, which are otherwise difficult to convey.
The Mail Abuse Prevention System (MAPS) is an organization that provides anti-spam support by maintaining a DNSBL. They provide five black lists, categorising why an address or an IP block is listed:
An email service provider (ESP) is a company that offers email marketing or bulk email services.
Backscatter is incorrectly automated bounce messages sent by mail servers, typically as a side effect of incoming spam.
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.
A cold email is an unsolicited e-mail that is sent to a receiver without prior contact. It could also be defined as the email equivalent of cold calling. Cold emailing is a subset of email marketing and differs from transactional and warm emailing.