Glossary

Quick definitions for terms you’ll see across this library. Each term opens site search for that word.

• A/B Testing — Comparing two versions of an email (subject line, content, send time) to see which performs better.
• Abandoned Cart Email — An automated message reminding a shopper to complete a purchase they left in their cart.
• Above the Fold — The portion of an email visible without scrolling, in the preview pane or on open.
• Alt Text — Descriptive text attached to an image that displays when images are blocked or read aloud by screen readers.
• Amazon SES — Amazon Simple Email Service — a cloud email-sending API often used for transactional mail and self-hosted ESPs.
• API Key — A unique credential used to authenticate requests to an email service provider's API.
• Authentication (Email Authentication) — Technical standards like SPF, DKIM, and DMARC that verify a sender's identity to mailbox providers.
• Autoresponder — An automated email triggered by a specific action or time delay.
• BIMI — Brand Indicators for Message Identification — a standard that can display a brand logo in supporting inboxes when DMARC is enforced.
• Blocklist (Blacklist) — A list of IP addresses or domains flagged as spam sources by mailbox providers or blocklist operators.
• Bounce Rate — The percentage of sent emails that were not delivered to the recipient's inbox.
• Broadcast Email — A one-time email sent to an entire list or segment, as opposed to an automated or triggered message.
• Bulk Sender — A sender who dispatches a high volume of email, subject to added authentication requirements from Gmail and Yahoo.
• CAN-SPAM Act — U.S. law setting rules for commercial email, including opt-out requirements and sender identification.
• Click Map — A visual overlay showing where recipients clicked within an email.
• Click-to-Open Rate (CTOR) — The percentage of opened emails that generated at least one click.
• Cohort Analysis — Grouping subscribers by a shared starting point, such as signup date, to compare their behavior over time.
• Cold Email — An unsolicited email sent to a recipient with no prior relationship, typically for outreach or sales.
• Complaint Rate — The percentage of delivered emails that recipients mark as spam or junk.
• Confirmation Email — A message verifying a subscriber's email address or a completed action, such as a signup or purchase.
• Contact List — A stored collection of subscriber email addresses and associated data used for sending campaigns.
• Conversion Rate — The percentage of email recipients who completed a desired action, such as a purchase or signup.
• CRM (Customer Relationship Management) — Software that tracks customer interactions and data, often integrated with email marketing platforms.
• Cross-Channel Marketing — Coordinating messaging across email, SMS, push, and other channels for a consistent customer experience.
• CSS Inlining — Converting stylesheet rules into inline HTML attributes so styles render consistently across email clients.
• CTR — Click-Through Rate — the percentage of email recipients who clicked one or more links in a message.
• Custom Field — A user-defined data point (e.g., first name, birthday) stored per subscriber and used for personalization.
• Dark Mode Email — Email content designed to remain readable and on-brand when viewed in a device's dark color scheme.
• Data Enrichment — Supplementing subscriber records with additional information from third-party or internal sources.
• Dedicated IP — An IP address used exclusively by one sender, giving them full control over their own sending reputation.
• Deliverability — The ability for legitimate email to reach the inbox rather than spam or promotions folders.
• Deliverability Audit — A review of sending practices, authentication, and reputation to diagnose and fix inbox placement issues.
• Deliverability Rate — The percentage of sent emails that successfully reach a recipient's inbox without bouncing.
• DKIM — DomainKeys Identified Mail — a cryptographic signature that proves an email was authorized by the sending domain.
• DMARC — Domain-based Message Authentication, Reporting, and Conformance — a policy that tells receivers how to handle SPF/DKIM failures and where to send reports.
• Domain Reputation — A score mailbox providers assign to a sending domain based on its historical sending behavior.
• Double Opt-In — A subscription process where a user confirms their email address before being added to a mailing list.
• Drip Campaign — A series of pre-scheduled emails sent automatically over time based on a trigger or schedule.
• Dynamic Content — Email content that changes per recipient based on data, behavior, or segment.
• Email Append — Adding email addresses to existing customer records using a third-party matching service.
• Email Cadence — The frequency and timing pattern at which emails are sent to subscribers.
• Email Client — The software or app used to read email, such as Gmail, Outlook, or Apple Mail.
• Email Copywriting — Writing persuasive, concise text for email subject lines, preview text, and body content.
• Email Engagement — A measure of how recipients interact with email, including opens, clicks, and replies.
• Email Fatigue — Subscriber disengagement caused by receiving too many emails too often.
• Email Frequency Cap — A limit on how many emails a subscriber can receive within a given time period.
• Email Gateway — A server or service that handles the sending and receiving of email between networks.
• Email Header — The metadata portion of an email containing routing, authentication, and sender information.
• Email List Rental — Paying to send a campaign to a third party's opted-in list, distinct from purchasing addresses outright.
• Email Marketing Funnel — The stages a subscriber moves through, from signup to purchase to retention, driven by email.
• Email Preview Text (Preheader) — The snippet of text shown after the subject line in an inbox preview.
• Email Rendering — How an email's layout, fonts, and images actually display across different clients and devices.
• Email Template — A reusable, pre-designed email layout that can be populated with new content for each send.
• Email Verification — Checking that an email address is valid and deliverable before adding it to a list or sending to it.
• Engagement Score — A composite metric ranking subscribers by how actively they open, click, and interact with email.
• ESP — Email Service Provider — a platform used to send, manage, and measure marketing or transactional email campaigns.
• Exit-Intent Popup — A signup form triggered when a visitor's cursor behavior suggests they're about to leave a page.
• Feedback Loop (FBL) — A system where mailbox providers notify senders when a recipient marks an email as spam.
• First-Party Data — Information a company collects directly from its own audience, such as purchase or browsing history.
• Funnel Stage — The point a subscriber occupies in a marketing funnel, such as awareness, consideration, or decision.
• Gmail Tabs — Gmail's inbox categorization feature that sorts incoming mail into Primary, Promotions, Social, and other tabs.
• Hard Bounce — A permanent delivery failure, often due to an invalid or non-existent email address.
• HTML Email — An email formatted with HTML markup to include styling, images, and layout, as opposed to plain text.
• Image Blocking — A mail client setting that prevents images from loading automatically until the recipient allows it.
• Inactive Subscriber — A contact who has not opened or clicked an email within a defined recent period.
• Inbox Placement — Whether an email lands in the primary inbox versus a spam or promotions folder.
• Interactive Email (AMP for Email) — Email that supports in-message actions like carousels, forms, or live content without leaving the inbox.
• IP Reputation — A score mailbox providers assign to a sending IP based on its sending history and behavior.
• ISP (Internet Service Provider) — A company providing internet access, sometimes also operating its own mail servers and spam filters.
• Junk Folder — A mail client folder where suspected spam or unwanted email is automatically routed.
• KPI (Key Performance Indicator) — A specific, measurable metric used to evaluate the success of an email program or campaign.
• Landing Page — The web page a subscriber arrives at after clicking a link in an email.
• Lapsed Subscriber — A contact who was previously engaged but has stopped opening or clicking over an extended period.
• Lead Magnet — A free resource (ebook, checklist, template) offered in exchange for an email address.
• Lifecycle Email — Automated messages tied to a customer journey stage such as welcome, onboarding, win-back, or renewal.
• List Churn — The rate at which subscribers unsubscribe, bounce, or become inactive over time.
• List Growth Rate — The net rate at which an email list gains new subscribers over a period.
• List Hygiene — Ongoing cleanup of invalid, inactive, or risky addresses to protect sender reputation and improve engagement.
• Mail Merge — Automatically inserting personalized data, such as a name, into a template to generate individual emails.
• Mailbox Provider (MBP) — A company that operates email infrastructure for recipients, such as Gmail or Outlook.
• Mailing List — A collection of email addresses that have opted in to receive communications from a sender.
• Marketing Automation — Software that triggers and manages email sequences based on subscriber behavior or data.
• Marketing Qualified Lead (MQL) — A contact whose engagement signals, often including email activity, indicate readiness for further marketing.
• Message-ID — A unique identifier assigned to each email, used for tracking and troubleshooting delivery.
• MJML — A markup language and framework for building responsive HTML emails with a simplified component syntax.
• Multivariate Testing — Testing multiple email elements at once, such as subject line and image, to see which combination performs best.
• Newsletter — A recurring email sent to subscribers containing curated content, updates, or news.
• Onboarding Sequence — A series of emails introducing a new user or customer to a product or service.
• One-Click Unsubscribe — A mechanism, required by Gmail and Yahoo for bulk senders, letting recipients unsubscribe in a single action.
• Open Rate — The percentage of delivered emails that were opened. Increasingly noisy due to Apple Mail Privacy Protection and similar features.
• Opt-Out — The action a recipient takes to stop receiving future email communications.
• Permission Marketing — An approach to marketing that relies on explicit subscriber consent before sending communications.
• Personalization — Adapting content, offers, or send timing to an individual recipient using known data and behavior.
• Postmaster Tools — Dashboards (e.g., Google Postmaster Tools) that let senders monitor domain reputation and delivery metrics.
• Preference Center — A page where subscribers can manage the type and frequency of emails they receive.
• Re-engagement Campaign — A series of emails targeting inactive subscribers to win back their attention or clean the list.
• Responsive Email — An email designed to render correctly across different screen sizes and devices.
• Seed List — A set of test inboxes across providers used to monitor placement, rendering, and deliverability.
• Segmentation — Splitting an audience into groups based on behavior, attributes, or preferences so messaging can be more relevant.
• Send Time Optimization — Using data or algorithms to determine the best time to send email to each subscriber.
• Sender Reputation — A score reflecting how trustworthy a sending domain or IP appears to mailbox providers.
• Single Opt-In — A subscription process that adds an address immediately after form submission without a confirmation email.
• Soft Bounce — A temporary delivery failure, such as a full inbox or a server timeout.
• Spam Trap — An email address used to identify senders with poor list hygiene, often set up by mailbox providers or blocklists.
• SPF — Sender Policy Framework — a DNS record that lists which servers are allowed to send email for a domain.
• Subject Line — The line of text that summarizes an email's content and appears first in an inbox.
• Subscriber — An individual who has opted in to receive email from a sender.
• Suppression List — A list of email addresses excluded from future sends, such as unsubscribes or bounces.
• Throttling — Deliberately limiting the rate of email sends to protect sender reputation.
• Time Zone Send — Sending an email based on each recipient's local time zone rather than a single send time.
• Transactional Email — Message triggered by a user action — password resets, receipts, shipping updates — rather than a marketing broadcast.
• Triggered Email — An email automatically sent in response to a specific subscriber action or event.
• Unsubscribe Rate — The percentage of recipients who opt out of a mailing list after receiving a campaign.
• UTM Parameters — Tags appended to links to track campaign performance in analytics tools.
• Warm-up — Gradually increasing send volume from a new domain or IP so mailbox providers learn to trust the sender.
• Welcome Email — The first automated email sent to a new subscriber after signup.
• Whitelist (Allowlist) — A list of trusted senders that mailbox providers or filters treat favorably.
• Win-back Campaign — An email sequence aimed at re-engaging subscribers who have gone inactive.
• XML Feed — A structured data file, sometimes used to power dynamic or catalog-based email content.
• Zero-Party Data — Information a customer proactively and intentionally shares with a brand, such as stated preferences.

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