Closed loop marketing
the process by which customer data can feed your marketing campaigns and drive up sales performance.
DomainKeys Identified Mail (DKIM)
DKIM is an email authentication protocol that enables the sender to use public-key cryptography to sign outgoing emails in a manner that can be verified by the receiver. The DKIM specification is based on the prior protocols Domain Keys and Identified Internet Mail. DKIM is defined in IETF RFC 4871. The DKIM standard is already being adopted by Gmail and other large corporations to completely eliminate phishing and spoofing from internet mail.
email authentication technology that verifies whether an email message originates from the domain name it claims to have been sent from . Ensuring a valid identity on an email has become a vital first step in stopping spam, forgery, fraud, and even more serious crimes. 
Internet Engineering Task Force (IETF)
the Internet Engineering Task Force is a large open international community of network designers, operators, vendors, and researchers concerned with the evolution of the Internet architecture and the smooth operation of the Internet. It is open to any interested individual. The goal of the IETF is to make the Internet work better.
Message Transfer Agent (MTA)
any system running SMTP routing software that can take a message, process it, look up destination information in DNS (or other routing table), and deliver to the intended receiving system. MTAs are typically server applications such as Sendmail, Microsoft Exchange, Postfix, Lotus Domino, qmail, PowerMTA, etc.
extension to the SMTP service that allows an SMTP server and client to use TLS (Transport Layer Security) to provide private, authenticated communication over the Internet. 
Sender Policy Framework (SPF)
SPF is a path-based email authentication protocol that allows email receivers to determine if the sender is authorized to use the domains in the message’s header by evaluating the IP address of the sender’s outbound MTA based on information published by the sender in DNS TXT records. SPF is defined in IETF RFC 4408.
Simple Mail Transfer Protocol (SMTP)
is an Internet standard for electronic mail (e-mail) transmission across Internet Protocol (IP) networks. SMTP was first defined by Jonathan Postel in IETF RFC 821 (1982), and last updated by IETF RFC 5321 (2008) which includes the extended SMTP (ESMTP) additions, and is the protocol in widespread use today. SMTP is specified for outgoing mail transport and uses port 25.
Transport Layer Security (TLS)
the TLS protocol provides communications security over the Internet. The protocol allows client/server applications to communicate in a way that is designed to prevent eavesdropping, tampering, or message forgery. TLS is an IETF standards track protocol, last updated in RFC 5246.
 RFC 3207 - SMTP Service Extension for Secure SMTP over Transport Layer Security
 2008 OTA State of the State of Email Authentication Report
 Email Authentication by David MacQuigg