Email spam, also known as junk email or unsolicited bulk email (UBE), is a subset of electronic spam involving nearly identical messages sent to numerous recipients by email.
A DNS-based Blackhole List (DNSBL) or Real-time Blackhole List (RBL) is an effort to stop email spamming. It is a “blacklist” of locations on the Internet reputed to send email spam.
Email spoofing is the creation of email messages with a forged sender address. It is easy to do because the core protocols do not have any mechanism for authentication. Spam and phishing emails typically use such spoofing to mislead the recipient about the origin of the message.
Domain-based Message Authentication, Reporting and Conformance (DMARC) is an email validation system designed to detect and prevent email spoofing.
DomainKeys Identified Mail (DKIM) is an email authentication method designed to detect email spoofing by providing a mechanism to allow receiving mail exchangers to check that incoming mail from a domain is authorized by that domain’s administrators.
Sender Policy Framework (SPF) is a simple email-validation system designed to detect email spoofing by providing a mechanism to allow receiving mail exchangers to check that incoming mail from a domain comes from a host authorized by that domain’s administrators.