Email Glossary

Every email marketing term you need to know, from A/B testing to webhooks. Bookmark this page and come back anytime.

A/B Testing: Sending two or more variations of an email (subject line, content, send time) to a small portion of your list, then sending the winning version to the rest.
Above the Fold: The portion of an email visible without scrolling. Critical for engagement since most recipients decide to keep reading based on this area.
Allowlist: A list of approved senders that bypass spam filters. Asking subscribers to add your address to their allowlist improves deliverability.
Authentication: Protocols (SPF, DKIM, DMARC) that verify you are authorized to send email from a domain, preventing spoofing and improving inbox placement.
Automation: A sequence of emails triggered by a specific event — such as a signup, purchase, or abandoned cart — sent automatically without manual intervention.

BIMI: Brand Indicators for Message Identification. A standard that lets you display your brand logo next to your emails in supporting inboxes.
Blocklist: A real-time database of IPs or domains identified as spam sources. Being on a blocklist severely impacts deliverability.
Bounce: An email that cannot be delivered. A hard bounce means the address is permanently invalid; a soft bounce is a temporary issue like a full inbox.
Bounce Rate: The percentage of sent emails that were not delivered. Keep below 2% to maintain sender reputation. Calculated as bounces / emails sent × 100.
Broadcast: A one-time email sent to a list or segment, such as a newsletter or promotional campaign. Unlike automations, broadcasts are manually scheduled.
BYOS (Bring Your Own SES): A model where you connect your own AWS SES account for sending, reducing email costs to roughly $0.10 per 1,000 emails instead of paying platform markup.

CAN-SPAM: U.S. law that sets rules for commercial email: requiring a physical address, a clear unsubscribe mechanism, and honest subject lines.
Click-Through Rate (CTR): The percentage of recipients who clicked at least one link in your email. Calculated as unique clicks / delivered emails × 100.
Complaint Rate: The percentage of recipients who marked your email as spam. Must stay below 0.1% to avoid reputation damage. ISPs monitor this closely.
Contact: An individual person in your email list, identified by their email address along with profile data like name, tags, and engagement history.
Conversion Rate: The percentage of email recipients who completed a desired action — a purchase, signup, or download — after clicking through.

Dedicated IP: An IP address used exclusively by one sender. Gives full control over sender reputation but requires consistent sending volume to maintain.
Deliverability: The ability to reach the inbox rather than the spam folder. Affected by sender reputation, authentication, content, list hygiene, and engagement.
DKIM: DomainKeys Identified Mail. A cryptographic signature added to email headers that proves the message was not altered in transit and was sent by the domain owner.
DMARC: Domain-based Message Authentication, Reporting & Conformance. A policy that tells receiving servers what to do when SPF or DKIM checks fail.
Double Opt-In: A subscription process where a new subscriber must confirm their email address by clicking a link in a verification email before being added to the list.
Drip Campaign: A series of automated emails sent on a schedule, often used for onboarding, nurturing, or education over days or weeks.
Dynamic Content: Email content that changes based on the recipient's data — name, location, purchase history, or segment membership — for personalized experiences.

Email Client: The software used to read email: Gmail, Outlook, Apple Mail, etc. Each renders HTML differently, making cross-client testing essential.
Email List: A collection of contacts who have opted in to receive your emails. The foundation of email marketing — quality matters more than quantity.
Engagement Score: A numeric rating of how actively a contact interacts with your emails — opens, clicks, purchases — used to segment active vs. disengaged subscribers.
ESP (Email Service Provider): A platform that provides tools for sending marketing and transactional emails, managing lists, building templates, and tracking analytics.

GDPR: General Data Protection Regulation. EU law requiring explicit consent for email marketing, the right to data access, and the right to be forgotten.

Hard Bounce: A permanent delivery failure — the email address does not exist or the domain is invalid. Hard-bounced addresses should be immediately removed.
HTML Email: An email formatted with HTML and CSS, allowing rich layouts, images, buttons, and branding. Most marketing emails are HTML-based.

Inbox Placement Rate: The percentage of delivered emails that land in the primary inbox rather than spam, promotions, or other folders.
Interest Group: A preference category that contacts can opt into — like product updates vs. blog posts — enabling more relevant email targeting.
IP Warm-Up: Gradually increasing sending volume on a new IP address to build reputation with ISPs. Rushing this process leads to spam folder placement.

List Hygiene: The practice of regularly cleaning your email list by removing invalid, bounced, and unengaged addresses to maintain high deliverability.

MJML: A markup language that simplifies creating responsive HTML emails. It compiles into cross-client-compatible HTML, avoiding manual table-based layouts.

Open Rate: The percentage of delivered emails that were opened. Tracked via a transparent pixel. Apple Mail Privacy Protection has reduced accuracy since iOS 15.
Opt-In: The act of a person giving explicit permission to receive emails from you. Required by law in most jurisdictions (GDPR, CAN-SPAM, CASL).

Personalization: Customizing email content using subscriber data — name, past purchases, location — to increase relevance and engagement.
Plain Text Email: An email with no HTML formatting — just text. Often used for transactional messages or to appear more personal and avoid spam filters.
Preheader: The preview text shown after the subject line in the inbox. Acts as a secondary subject line and significantly impacts open rates.

Revenue Attribution: Tracking which email campaign or automation drove a purchase, typically using a click-based attribution window (e.g., 7 days).

Segment: A subset of your contact list filtered by specific criteria — behavior, demographics, purchase history — for targeted messaging.
Sender Identity: The verified email address or domain you send from. Must be authenticated with SPF and DKIM to ensure deliverability.
Sender Reputation: A score assigned by ISPs based on your sending history — bounce rates, complaints, engagement. Determines whether your emails reach the inbox.
SES (Simple Email Service): Amazon Web Services' email sending infrastructure. Highly scalable and cost-effective at $0.10 per 1,000 emails.
SMTP: Simple Mail Transfer Protocol. The standard protocol for sending emails between servers. ESPs and transactional services use SMTP or API-based sending.
Soft Bounce: A temporary delivery failure — the mailbox is full, the server is down, or the message is too large. Retried automatically a few times before giving up.
SPF: Sender Policy Framework. A DNS record that lists which servers are authorized to send email on behalf of your domain.
Suppression List: A list of email addresses that must not receive emails — bounces, complaints, and manual unsubscribes. Checked before every send.

Tag: A label applied to a contact for organization and segmentation. Tags can be added manually, via automations, or through integrations.
Transactional Email: An email triggered by a user action — order confirmation, password reset, shipping notification. Sent via API, not subject to marketing opt-in rules.
Trigger: The event that starts an automation — a form submission, a purchase, a tag being added, a date, or a webhook. The entry point of any automated workflow.

Unsubscribe Rate: The percentage of recipients who opted out after receiving an email. A rate above 0.5% per campaign suggests content or frequency issues.

Warm IP: An IP address with an established sending history and positive reputation. Warm IPs get better inbox placement than cold ones.
Webhook: An HTTP callback triggered by an event — email delivered, opened, clicked, bounced. Used to sync email activity with external systems in real time.

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