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A/B Test

A method of comparing two versions of an email to determine which one performs better in terms of metrics like open rate, click-through rate, or conversion rate.

Abandoned Cart Email

An automated email sent to customers who have added items to their shopping cart but did not complete the purchase. This email often includes the items left in the cart and may offer incentives like discounts to encourage completion of the purchase.

Acceptance Rate (Deliverability Rate)

The percentage of sent emails that are accepted by mail servers. A high acceptance rate is generally a positive indicator of good email deliverability.


The design of email content to be usable by as many people as possible, including those with disabilities. This can involve the use of alt text for images, readable fonts, and logical content structure.


A list of approved email addresses or IP addresses from which emails will be accepted. Being on an allowlist typically ensures better email deliverability.

Alt Text

Short for "alternative text," it is the text description for images in an email. Alt text is displayed when the image cannot be loaded and is also used by screen readers for accessibility.

AMP Emails

Stands for "Accelerated Mobile Pages for Email." AMP emails allow for interactive and dynamic content within the email itself, such as forms and carousels, without requiring the recipient to click through to a web page.

Animated GIF

A type of image file that includes multiple images or "frames" that are displayed in a sequence to create an animation. Animated GIFs can be used in emails to draw attention or convey information in a more engaging way.


Stands for "Application Programming Interface." In the context of email marketing, APIs allow for the integration of different software platforms, enabling tasks like automatically adding new subscribers to an email list or triggering transactional emails based on user behavior.

Apple Mail Privacy Protection (AMPP)

A feature in Apple's Mail app that prevents senders from knowing when an email is opened, and hides recipients' IP addresses. This has implications for metrics like open rates.

Bayesian Filter

A type of spam filter that uses Bayesian statistical methods to classify emails as spam or not spam based on their content and other attributes.

Behavioral Email

An email sent based on the recipient's behavior or interaction with a website or app. Examples include cart abandonment emails, browse abandonment emails, and post-purchase follow-up emails.


Stands for "Brand Indicators for Message Identification." It's a standard that allows brands to display their logo in the recipient's inbox, next to the email subject line, as a way to prove the email's authenticity.


A list of email addresses, domains, or IP addresses that are blocked from sending emails to a particular server or inbox. Being on a blocklist can severely impact email deliverability.

Bounce Rate

The percentage of sent emails that could not be delivered to the recipient's inbox. Bounces can be categorized as "hard" (permanent failure, such as an invalid email address) or "soft" (temporary failure, such as a full inbox).


In email marketing, this term refers to design elements that will display as intended across multiple email clients and platforms, ensuring a consistent user experience.

Bulk Mail

Emails sent to multiple recipients at once, often for marketing purposes. Bulk mail can be legitimate but is sometimes categorized as spam if not properly managed.


Stands for "Controlling the Assault of Non-Solicited Pornography And Marketing Act of 2003." It's a U.S. law that sets rules for commercial emails, including requirements for opt-out mechanisms and truthful subject lines.


A rotating set of images or content blocks within an email, allowing the user to swipe or click through multiple items without leaving the email.


Stands for "California Consumer Privacy Act." A law that enhances privacy rights and consumer protection for residents of California, USA. It has implications for email marketing, particularly around data collection and storage.


In HTML email design, cellpadding is the space between the cell wall and the cell content. It's used to control the appearance and layout of tables in emails.

Click-to-Open Rate (CTOR)

A metric that measures the effectiveness of the email content by dividing the number of unique clicks by the number of unique opens, usually expressed as a percentage.

Clickthrough Rate (CTR)

The ratio of users who click on a specific link in an email to the number of total users who view the email, usually expressed as a percentage.

Conditional Code

Code used in email templates to provide different experiences based on conditions like the recipient's email client or device.

Consent (Express and Implied)

Permission given by email recipients to receive communications. Express consent is explicit permission, usually through a sign-up form. Implied consent is inferred from actions, such as a completed purchase.


An individual on an email list who has opted in to receive email communications. Contacts can be further segmented based on various criteria like behavior, demographics, or engagement level.

Content Delivery Network (CDN)

A system of distributed servers that deliver web content, including images used in emails, based on the geographic location of the user, to speed up load times.

Customer Data Platform (CDP)

A type of software that creates a unified database of customer information that can be accessed and used by other systems, including email marketing platforms.

Customer Relationship Management (CRM)

Software that manages a company's interactions with current and potential customers. In email marketing, CRM systems can be integrated to automate and personalize email campaigns based on customer data.

Dark Mode

A display setting that changes the background to dark and text to light, reducing eye strain. Email designs may need to be optimized for dark mode to ensure readability and visual appeal.

Dedicated IP

An IP address used by a single sender for email campaigns, as opposed to a shared IP used by multiple senders. A dedicated IP can improve deliverability if managed well.

Delivery Rate

The percentage of emails sent that actually reach the recipient's server, whether or not they make it to the inbox. It's a basic measure of deliverability.


The act of sending out an email campaign to a list of recipients.


Stands for "DomainKeys Identified Mail." It's an email authentication method that helps prevent email spoofing, improving deliverability.


Stands for "Domain-based Message Authentication, Reporting, and Conformance." It's an email authentication protocol that uses SPF and DKIM to protect email domains from spoofing and phishing attacks.


An HTML document type declaration that defines the version of HTML being used in the email. It helps browsers to display the email correctly.

Double Opt-In

A subscription method where the user must confirm their email address after signing up, usually by clicking a link in a confirmation email. This ensures that the email address is valid and that the user genuinely wants to subscribe.

DPO (Data Privacy Officer)

A role within an organization responsible for ensuring that data collection and storage practices are compliant with privacy laws like GDPR.

Drip Campaign

A series of automated emails sent to specific segments of an email list, triggered by certain actions or timelines. Drip campaigns are designed to nurture leads and engage customers over time.

Dynamic Content

Content within an email that changes based on the recipient's behavior, preferences, or other personal data. This allows for a more personalized and relevant email experience for each individual recipient.

Email Body

The main content area of an email, which includes text, images, links, and other elements designed to communicate the message to the recipient.

Email Campaign

A coordinated set of individual email messages that are deployed across a specific period for a specific purpose.

Email Client

Software or a web application used to access and manage a user's email. Examples include Outlook, Gmail, and Apple Mail.

Email Editor

A tool within an Email Service Provider that allows for the design and layout of email templates, often with drag-and-drop functionality.

Email Framework

A pre-designed template or set of HTML/CSS rules that serve as the foundation for creating email designs. Frameworks can speed up the email design process and ensure consistency.

Email Harvesting

The unethical practice of collecting email addresses, often through automated means like scraping websites, without the consent of the email owner.

Email Preview

A feature within Email Service Providers that allows marketers to view how an email will appear in various email clients and devices before sending.

Email Service Provider (ESP)

A company that offers email marketing or bulk email services. ESPs provide tools for designing, sending, and tracking email campaigns.

Email Validation

The process of verifying that an email address is valid and deliverable. This is often done during the list-building phase to improve deliverability.

Email Verification

A step in the subscription process where the user must confirm the validity of their email address, often through a confirmation email. This is also known as double opt-in.

Email Weight

The total size of an email, including all text, images, and attachments. Emails that are too "heavy" may load slowly or not at all, affecting user experience and engagement.


In email marketing, this refers to how recipients interact with an email, including metrics like open rate, click-through rate, and time spent reading the email.


A design or content element that is displayed when the primary element cannot be rendered, such as a text description that appears when an image fails to load.


An email that is incorrectly identified as spam by spam filters, even though it is a legitimate communication.

Fluid/Hybrid Design

An email design approach that ensures content will render well on both desktop and mobile devices, without requiring separate designs for each.

Font Stack

A list of fonts in CSS that are applied in order of preference. If the first font is not available on the recipient's device, the next font in the stack is used.

Friendly From

The name that appears in the "From" field of an email, which can be different from the actual email address. It's used to identify the sender in a way that is recognizable to the recipient.

From Address

The email address that appears in the "From" field, indicating who the email is from. This address should be verified and consistent to improve deliverability and trust.


Stands for "Generally Accepted No-Gos in Advertising." These are practices that are generally considered unacceptable in email marketing, such as misleading subject lines or hidden unsubscribe links.


Stands for "General Data Protection Regulation." A regulation in EU law that protects the privacy and personal data of individuals within the European Union and the European Economic Area.

Ghost Table

In HTML email design, a table that is invisible but used to control the layout of the email in certain email clients.


Stands for "Graphics Interchange Format." A bitmap image format that supports both static and animated images. GIFs are commonly used in emails to add motion and attract attention.

Hard Bounce

An email that has been returned to the sender because the recipient's address is invalid, either because it doesn't exist or because the server has blocked delivery. Hard bounces are permanent failures.


The top section of an email that usually contains the logo, navigation links, and sometimes a preheader text. It sets the tone for the email and is often consistent across different email campaigns.


A decoy email address or form field used to catch spammers. It's hidden from regular users but visible to automated scripts, which may fill it out, revealing themselves as spam sources.

Image Blocking

The practice by some email clients of not automatically displaying images in emails, requiring the user to manually enable them. This can affect how the email is initially viewed and its engagement metrics.

Image Validation

The process of checking and optimizing images for email to ensure they display correctly across different email clients and don't slow down the loading time.

Image-Only Email

An email that consists primarily or entirely of images, with little to no text. This approach can create deliverability and accessibility issues.


Stands for "Internet Message Access Protocol." It's a standard email protocol that stores email messages on a mail server and allows the end user to view and manipulate the messages as though they were stored locally.

Inbox Display

How an email appears in the recipient's inbox, including the "From" name, subject line, and preheader text.

Inbox Placement Rate

The percentage of sent emails that actually land in the recipient's inbox as opposed to the spam folder or other locations.

Inbox Service Provider (ISP)

A company that provides email services, including the receiving, storing, and delivering of email messages. Examples include Gmail, Yahoo Mail, and Outlook.

Inline CSS

CSS styles that are applied directly within the HTML tags, rather than in a separate stylesheet. This is commonly used in email design to ensure styles render correctly across different email clients.

Interactive Email

An email that includes elements the recipient can interact with within the email itself, such as forms, carousels, or clickable tabs. This often uses advanced techniques like AMP for Email.

IP Warming

The practice of gradually increasing the volume of email sent through a new IP address to establish a good sender reputation and improve email deliverability.


A collection of email addresses used in email marketing campaigns. Lists can be segmented based on various criteria like behavior, demographics, or engagement level.

List Building

The process of adding new email addresses to an email marketing list, usually through methods like sign-up forms, social media, or partnerships.

List Churn

The rate at which email addresses leave an email list due to unsubscribes, bounces, or other factors. A high churn rate can indicate problems with list quality or engagement.

List Fatigue

A condition where recipients become less responsive to email marketing messages due to overexposure or lack of relevance, often leading to lower engagement metrics.

List Growth

The increase in the size of an email list over time, usually measured as a percentage of new subscribers.

List Hygiene

The practice of maintaining a clean email list by removing invalid addresses, duplicates, and unengaged subscribers to improve deliverability and engagement.

Mail Delivery Agent (MDA)

A software component that receives incoming email from the Mail Transfer Agent (MTA) and delivers it to the recipient's mailbox.

Mail Merge

A process that allows for the mass customization of emails by automatically inserting specific data fields like the recipient's name, company, or other personalized information.

Mail Submission Agent (MSA)

A software component that acts as the initial receiving point for email clients looking to send email. It queues the emails for the Mail Transfer Agent (MTA) to process.

Mail Transfer Agent (MTA)

A software component that routes and delivers email from one server to another. It works in conjunction with the Mail Submission Agent (MSA) and Mail Delivery Agent (MDA).

Mail User Agent (MUA)

The client-side software or application used by the end-user to access and manage their email, such as Microsoft Outlook or Mozilla Thunderbird.

Mailbox Provider (MBP)

A service that hosts and delivers email for end-users. Examples include Gmail, Yahoo Mail, and corporate email servers.

Marketing Automation Platform (MAP)

A software platform that automates various marketing tasks and workflows, including email marketing, lead nurturing, and customer segmentation.

Media Query

In CSS, a technique used to apply different styles depending on the characteristics of the device rendering the content, commonly used in responsive email design.

Merge Tag

A placeholder in an email template that gets replaced by specific content when the email is sent, allowing for personalization at scale.

MIME (Multi-Purpose Internet Mail Extensions)

A standard that extends the format of email to support text in character sets other than ASCII, as well as attachments of audio, video, images, and application programs.

Minify (HTML/CSS)

The process of removing unnecessary characters from code to reduce its size and improve load times, commonly used in email to improve performance.


Stands for "Mailjet Markup Language." It's a markup language designed to reduce the pain of coding responsive emails, making the process quicker and more foolproof.

Modular Email Design

An approach to email design that uses reusable blocks or modules to create a variety of email layouts, improving efficiency and consistency.

MX Record

Stands for "Mail Exchange Record." It's a DNS record that specifies the mail server responsible for receiving email messages on behalf of a domain.


A regularly distributed email campaign that is generally about one main topic of interest to its subscribers. Newsletters can be used for various purposes, including engagement, education, and sales.

No-Reply Address

An email address that is not monitored for incoming messages, often used for transactional emails. It's generally considered a best practice to avoid using no-reply addresses in email marketing.

Nurture Track/Nurture Sequence

A series of automated emails aimed at nurturing leads or engaging existing customers. These emails are typically educational or value-based rather than promotional.

Onboarding Emails

A series of emails sent to new subscribers or customers to welcome them, provide useful information, and guide them through initial steps.

Open Rate

Traditionally calculated as the percentage of emails that are opened by recipients, divided by the total number of emails sent, minus the number of bounces. However, this metric has limitations due to the unreliability of tracking methods. Many email clients block tracking pixels or auto-load images, making it difficult to accurately measure opens. Additionally, privacy measures like Apple Mail's Privacy Protection can further obscure true engagement levels. As such, open rate should be considered an approximate indicator of engagement rather than an absolute measure.


Opt-in refers to the explicit permission given by individuals to receive email communications. Opt-out refers to the process by which individuals can unsubscribe from receiving further communications.


Stands for "Payment Card Industry." In the context of email marketing, PCI compliance is crucial when sending transactional emails that might include payment or other sensitive information.


The practice of tailoring email content to individual recipients based on their preferences, behavior, or other personal data.

Personally Identifiable Information (PII)

Information that can be used to identify an individual, such as name, email address, or phone number. PII must be handled carefully to comply with privacy laws.

Plain Text Email

An email that contains only text and no HTML or rich media elements. Plain text emails are often sent along with HTML emails as a fallback.


Stands for "Post Office Protocol." It's an older email standard used to retrieve messages from a remote server to a local client, removing them from the server in the process.


An individual or role responsible for managing an email system or server, often tasked with ensuring deliverability and compliance with email standards and laws.

Preference Center

A web page where email subscribers can manage their subscription preferences, including frequency, topics, and format.

Preheader Text (Preview Text)

A snippet of text that appears next to or below the subject line in the recipient's inbox, providing a preview of the email content.

Preview Pane

A feature in some email clients that allows users to view the content of an email without actually opening it.

Privacy Policy

A statement that discloses how a company collects, uses, and manages the data of its customers, including how the data may be used for email marketing.

Progressive Profiling

A technique where additional data about a lead or customer is gradually collected over time, often through dynamic forms or behavioral tracking, to improve personalization and targeting.

Promotional Email

An email sent with the aim of promoting a product, service, or event. Unlike transactional emails, promotional emails are commercial in nature and generally require explicit consent from the recipient.

Pseudo Element

In CSS, a keyword added to a selector that lets you style a specific part of the selected element(s). In email, pseudo elements are often used for advanced styling but may not be supported in all email clients.


In the context of email, this refers to emails that are temporarily held by an email security program or spam filter to determine whether or not they are spam.

Re-Engagement Campaign

A series of emails sent to inactive or less-engaged subscribers with the goal of rekindling interest and encouraging interaction with the brand.

Read, Skim, Glance/Delete

A framework for understanding how recipients interact with emails. "Read" indicates thorough engagement, "Skim" suggests a quick overview, "Glance" implies minimal attention, and "Delete" means the email was not engaged with at all.


The individual or email address that is the intended receiver of an email.


The process by which email clients display the HTML and CSS code of an email, converting it into a visual format for the end-user.

Reply-to Address

The email address that receives replies from the recipient. It is generally considered best practice to use a monitored address to encourage interaction.

Responsive Design

An approach to email design that ensures emails render well on various screen sizes by using fluid grids, flexible images, and CSS media queries.

Seed List

A list of internal or test email addresses used to gauge deliverability and appearance of an email before it is sent to the main list.


The practice of dividing an email list into smaller groups based on specific criteria, such as demographic information or engagement levels, to send more targeted and relevant content.

Semantic HTML

HTML that introduces meaning to the web page rather than just presentation. For example, using <header>, <footer>, and <article> tags to indicate the role of the content.


The individual, company, or email address that sends an email.

Sender Name

The name that appears in the "From" field in the recipient's inbox. It can be a person's name, a company name, or a combination of both.

Sender Reputation

A score assigned to an outgoing mail server by recipient mail servers, based on the quality of the email traffic and other factors like spam complaints and engagement rates.

Shared IP

An IP address used by multiple senders. The reputation of a shared IP is affected by the actions of all users, making it potentially less reliable for email deliverability compared to a dedicated IP.


Stands for "Simple Mail Transfer Protocol." It's the standard protocol for sending email messages between servers.


Short pieces of reusable code or text that can be inserted into larger coding projects, including email templates.

Soft Bounce

An email that is returned to the sender because of a temporary issue, such as a full inbox or a down server. Unlike hard bounces, soft bounces are generally resolvable.

Spam Trap

An email address used to catch spam. These addresses are monitored by organizations and ISPs, and sending to them can result in being blacklisted.


Unsolicited, irrelevant, or inappropriate email messages sent over the internet, typically to a large number of users, for the purposes of advertising, phishing, spreading malware, etc.


A spam filter used by email providers to identify and filter out spam based on a set of rules.


Stands for "Sender Policy Framework." It's an email authentication method designed to detect and block email spoofing by providing a mechanism to allow receiving mail exchangers to verify that incoming mail comes from a domain authorized by that domain's administrators.


The act of disguising a communication from an unknown source as being from a known, trusted source, often used in phishing attacks.

Subject Line

The line of text that serves as the heading of an email, displayed in the recipient's inbox. It's a crucial element as it often determines whether the email is opened.


An individual who has opted-in to receive email communications from a brand or organization.

Suppression List

A list of email addresses that have been removed from the main mailing list, either because they have unsubscribed, marked emails as spam, or have been identified as invalid or temporary addresses.

Table Role

In HTML email design, the role attribute can be added to a table to improve accessibility by indicating how the table should be interpreted.


A pre-designed layout for an email, often including placeholders for content and images, which can be used multiple times.

Text-to-Image Ratio

The proportion of text to images in an email. A balanced ratio is important for deliverability and accessibility.


The practice of limiting the number of emails sent in a given time frame to avoid overwhelming the server or triggering spam filters.

Tracking Pixel

A small, invisible image embedded in an email that allows the sender to track opens and other engagement metrics.

Transactional Email

An email sent to an individual based on a specific action or transaction, such as a purchase confirmation or password reset. These emails are generally exempt from opt-in laws but must still be relevant to the transaction.

Trigger Email

An automated email sent based on specific criteria or events, such as a subscriber's birthday or a product back in stock notification.

Unique Opens

The number of individual recipients who have opened an email, regardless of how many times each person has opened it.

Unsolicited Commercial Email (UCE)

Emails that are sent without explicit permission from the recipient, often considered as spam. Sending UCE can lead to legal consequences and damage to sender reputation.

Unsubscribe Link

A link provided in every commercial email that allows recipients to opt-out of future emails from the sender. Including an easily accessible unsubscribe link is a legal requirement in many jurisdictions.

Unsubscribe Rate

The percentage of recipients who click the unsubscribe link in an email, calculated by dividing the number of unsubscribes by the total number of emails delivered. A high unsubscribe rate can indicate content or frequency issues.

Web Fonts

Fonts that are downloaded from the web when an email is opened, allowing for more design flexibility compared to standard system fonts. However, not all email clients support web fonts.


An email service that is accessed via a web browser, as opposed to an email client that downloads messages to a computer. Examples include Gmail, Yahoo Mail, and

Welcome Series

A sequence of emails sent to new subscribers or customers, usually automated, with the aim of engaging them, providing useful information, and setting the tone for future communications.


Stands for "What You See Is What You Get." An interface that allows users to create and edit emails while viewing a version that closely resembles the end result. It's commonly used in Email Service Providers for users who may not be familiar with HTML or CSS.