Email Marketing Glossary

A/B Split testing

In A/B Split testing, subscribers are divided into two equal segments. Each of these segments can be tested with different variables, such as diffferent subject headings or email content, to see which approach is more effective.


In email marketing, autoresponders are automated messages that are scheduled to be sent at specific times, such as welcome messages, follow-up messages or other date-based email communication. An autoresponder can be sent as a single email, or can be sequenced over time (drip campaign).


The amount of information that can be transmitted over the Internet in a specific amount of time.


Blacklists are made up of lists of IP addresses belonging to organizations that have been identified as senders of SPAM. Blacklists are often used by ISPs and corporations as part of the filtering process that determines which IP addresses they prohibit from sending mail to their members.


When emails are prevented from reaching their intended destination, typically due to action taken on the part of the Internet Service Provider (ISP).


A "Bounced" email indicates that an attempt to deliver an email to a particular address has failed. This may occur if the email address is no longer valid or the intended recipient's ISP and/or email servers were not functioning over a period of 3 consecutive days.

Bounce - Hard

An email address that is rejected for a permanent reason that cannot be resolved, such as: "the address does not exist".

Bounce - Soft

An email address that is rejected for what is most likely a temporary reason, such as an overfilled inbox. A soft bounce is an email message that gets to the recipient's mail server but is returned undelivered before it reaches the recipient. A soft bounce might occur because the recipient's inbox is full.


The CAN-SPAM Act of 2003 (Controlling the Assault of Non-Solicited Pornography and Marketing Act) is a federal law that establishes requirements for those who send commercial email. It spells out penalties for spammers and companies whose products are advertised in spam if they violate the law, and gives consumers the right to ask emailers to stop spamming them. Among other measures, the law:

  • Bans false or misleading header information. Your email's "From," "To," and routing information – including the originating domain name and email address – must be accurate and identify the person who initiated the email.
  • Prohibits deceptive subject lines. The subject line cannot mislead the recipient about the contents or subject matter of the message.
  • Requires that your email give recipients an opt-out method. You must provide a return email address or another Internet-based response mechanism that allows a recipient to ask you not to send future email messages to that email address, and you must honor the requests. Any opt-out mechanism you offer must be able to process opt-out requests for at least 30 days after you send your commercial email.
  • It requires that commercial email be identified as an advertisement and include the sender's valid physical postal address. Your message must contain clear and conspicuous notice that the message is an advertisement or solicitation and that the recipient can opt out of receiving more commercial email from you. It also must include your valid physical postal address.

The CAN-SPAM Act also provides for penalties for a number of other offenses, which can be reviewed here:


A Completely Automated Public Turing test to tell Computers and Humans Apart is used to determine whether or not the user is human. Users are asked to type in a series of distorted images to prove that they are not a machine.


Content Delivery Network, also known as a content distribution network. A CDN is a large distributed system of servers deployed in multiple data centers on the Internet. The goal of a CDN is to serve content to end users with high availability and high performance. CDNs serve a large fraction of the Internet content today, including web objects (text, graphics, and scripts), downloadable objects (media files, software, documents), applications (e-commerce, portals), live streaming media, and social networks.

Click-through Rate (CTR), Click Rate

The percentage of recipients that click on a link enclosed in the email. To determine the click-through rate, divide the number of responses by the number of emails sent (multiply this number by 100 to express the result as a percentage).

Confirmed Opt-in

"Confirmed opt-in", also known as "double opt-in" provides an extra layer of security by requiring that an email account be both subscribed and then verified by a confirmation email before it is added to the list. As a result, only those people with access to the account can respond to the confirmation message, greatly reducing the chance of abuse. it is regarded as the gold standard for secure email marketing.

Conversion Rate

A metric which measures the percentage of people converted into subscribers or buyers out of the total population exposed to a particular campaign.


The ability of the email sender to consistently deliver an email to a recipient's inbox with HTML and text intact. Marketers operating permission-based email schemes need to carefully consider deliverability due to aggressive SPAM filters.

DKIM: DomainKeys Identified Mail

An anti-spam software application that uses a combination of public and private keys to authenticate the sender's mail domain and reduce the chance that a spammer will fake the domain sending address.


Similar to DKIM. An anti-spam software application that uses a combination of public and private keys to authenticate the sender's domain (A name by which a computer connected to the Internet is identified) and reduce the chance that a spammer will fake the domain sending address.

Double Opt-in

"Double opt-in", also known as "confirmed opt-in", requires that email accounts be both subscribed and then verified by a confirmation email before they are added to the list.

Hard Bounced Email

A hard bounce is an e-mail message that has been returned to the sender because the recipient's address is not valid. A hard bounce might occur because the domain name doesn't exist or because the recipient is unknown.


The header in an email is the part of the email that is not visible to the recipient unless they have their "View Headers" turned on. This tells the recipient what servers the email is coming from and what programs are being used to generate the email. Headers contain information on the email itself and the route it's taken across the Internet.

Hosted Email

A hosted version of an email allows users to view the email message as a web page, thus ensuring that all formatting remains intact.

House List

A permission-based list that you build yourself.  Your house list is one of your most valuable assets.

HTML Email

HTML email is created with HTML, which allows the display of images as opposed to simple text. Ninety five percent of all email readers have the ability to display HTML emails, which are more visually appealing than mere text.  Many readers have the default where images are "turned off" or not viewable by the recipient. For this reason you need to make sure your recipients add you to their address book so you'll always go into the inbox where images will show.

IP Address

The Internet Protocol IP) address is a computer's address or domain name, expressed numerically. An IP address in general looks like this:

Landing Page

The page on a website where the visitor arrives (which may or may not be the home page). In terms of an email campaign, if a user wants to track a campaign separately, they set up an additional page for recipients to visit. This way they can track distinctive traffic to this page from their email.

Load Time

The length of time it takes for a page to open completely in the browser window. You'll want your load time to be as fast as possible.

Multi-part MIME Email

Multipurpose Internet Mail Extensions (MIME) is an Internet standard for the format of email. Virtually all Internet email is transmitted in MIME format. This simply means that two versions of the email are sent, one graphical and one text. The appropriate version is then directed to the recipient based on the recipient's email client's preferences.

Open Rate

The number of HTML message recipients who opened your email, typically measured as a percentage of the total number of emails sent, although calculation methods may differ. The open rate is a useful metric for judging response to an email campaign but it should be noted that open rates for text emails can't be calculated.

Open Relay

An open relay is an email server configured so that anyone on the internet can dispatch email. Once an acceptable means of sending email in the past, spammers have used open relay to re-route their email through a third party to avoid detection. The CAN SPAM Act of 2003 made it illegal to send spam through an open relay.


Opting-In is the action a person takes when he or she actively agrees, by email or other means, to receive communications from an email sender.

Opt-in form

A form that website owners can add to their site to collect newsletter signups from visitors.


Opt-out email marketing assumes the recipient wants to receive email unless they specifically ask to be removed from the list – in other words, "opt-out" or "unsubscribe". If readers fail to state explicitly that they no longer wish to remain on the list, they can expect to receive messages until they make their desire known. Response rates tend to be lower when sending opt-out email, so be prepared for this result when you're analyzing your campaigns.


When offering customers further information, such as a whitepaper or article via a link in an email, the payoff is the information they gain access to when clicking on that link.

Permission-based email

The practice of only sending email messages to those recipients who have agreed to receive them.


Customizing an email to make it more personal for the recipient. This might include using the recipient's name in the salutation, referring to previous purchases or correspondence, or offering recommendations based on previous buying patterns.


In a phishing scam, a spammer poses as a trusted party, such as a bank or reputable online vendor. The spammer sends email messages directing recipients to Web sites that appear to be official but are actually fraudulent. Visitors to these Web sites are asked to disclose personal information, such as credit card numbers, or to purchase counterfeit or pirated products. See also: Sender-ID, Spoofing


Sender-ID is an email industry initiative championed by Microsoft and other industry leaders as a technical solution to help counter spoofing—the #1 deceptive practice used by spammers. See also: Phishing, Spoofing

Single Opt-in

Under single opt-in formats, businesses only mail addresses that have been actively subscribed to their list, typically by completing a web form, filling out a business reply card or sending an email to a specific address. Because the registration process is proactive, a single-opt in policy offers a higher level of security than the opt-out approach, but also has the following limitations:

  • Since single opt-in procedure does not require email address verification, it is possible to register other people without their consent, merely by having knowledge of that person's email address.
  • A mistyped address or the entry of a bogus email account that happens to belong to someone else can result in a company mailing a customer who has not registered to receive messages.
  • Single opt-in email policies are susceptible to spam traps. Spam traps are essentially email addresses or domains that have not registered to receive any email. Therefore, any messages they do receive must be spam. The problem for marketers comes when people deliberately subscribe spam trap addresses to their lists, or one is inadvertently added. This scenario exposes the mailer to blacklisting by ISPs or the organization operating the spam trap.
Spam Trap

A spam trap is a seemingly valid email address used to identify spam messages. The idea is to take an address that hasn't been subscribed to any email lists and monitor the email it receives. As it wasn't subscribed to any email, anything it receives must be unsolicited (spam).


SPAM or Unsolicited Commercial Email (UCE) is unsolicited email, particularly of a commercial nature. Sending email to people who have not requested to receive messages from you will likely result in SPAM complaints.

SPF (Sender Policy Framework)

An email authentication system that verifies that a message came from an authorized mail server. SPF is designed to detect messages from spammers and phishers who falsify the sender's IP address in the email header.


Email spoofing involves forging a sender's address on email messages. It can be used by malicious individuals to mislead email recipients into reading and responding to deceptive mail. These fake messages can jeopardize the online privacy of consumers and damage the reputation of the companies purported to have sent the messages. Spoofed email often contains phishing scams. See also: Phishing, Sender-ID

Suppression List

A list of addresses that is never sent emails. When a campaign is launched, addresses on the suppression list are automatically removed from the mailing list for that campaign. These lists are used for CAN SPAM compliance as well as segmenting different recipients.


Sending messages to users who are most likely to be receptive, based on their geographic, demographic, psychographic and behavioral characteristics.

Unique Forwarders

The number of unique individuals who forward an email. When the number of unique forwards is totaled, each person that forwards a particular email is counted just once, no matter how many times they forward that message.

Variable Envelope Return Paths (VERP)

The method of using a different envelope return / reply path for each recipient of an email message to ensure that the correct address is always processed in the case of an unsubscribe or bounce.

Web-friendly Fonts

Almost all web browsers are capable of displaying four primary fonts properly: Times, Arial, Helvetica, and Verdana, as well as their variants (Arial Narrow, Times New Roman, etc.).


Whitelists are lists of commercial emailers who have been approved to send mail through the ISP. The ISP requires a list of IP addresses that email will be sent from, and in some cases a test period where the commercial emailer will be approved or rejected.

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