Email Marketing Glossary

A

A/B Testing

A method of sending two versions of an email to a small portion of your list to see which performs better before sending the winner to the rest. Common variables include subject lines, sender names, and email content.

Authentication

A set of technical standards (SPF, DKIM, DMARC) that verify your emails are genuinely coming from your domain. Proper authentication improves deliverability and protects your brand from spoofing.

B

Bounce Rate

The percentage of emails that could not be delivered to the recipient's inbox. Hard bounces are permanent failures (invalid address); soft bounces are temporary (full inbox, server issue).

Broadcast Email

A single email sent to an entire list or segment at the same time - as opposed to automated or triggered emails that send based on subscriber behavior.

C

Click Rate

The percentage of delivered emails where the recipient clicked at least one link. Also called Click-Through Rate (CTR). A key indicator of how engaging your email content is.

Click-to-Open Rate (CTOR)

The percentage of people who opened your email and then clicked a link. This measures the effectiveness of your email content independently of your subject line.

Complaint Rate

The percentage of recipients who marked your email as spam. A complaint rate above 0.1% is considered high and can damage your sender reputation with inbox providers.

D

Deliverability

The ability of your emails to reach subscribers' inboxes rather than spam folders. Deliverability is influenced by sender reputation, authentication, list quality, and email content.

DKIM (DomainKeys Identified Mail)

An email authentication method that adds a digital signature to your outgoing emails. Receiving servers use this signature to verify that the email was not altered in transit and genuinely came from your domain.

DMARC (Domain-based Message Authentication)

A policy that tells receiving mail servers what to do if an email fails SPF or DKIM checks - reject it, quarantine it, or do nothing. DMARC protects your domain from being used in phishing attacks.

Double Opt-in

A subscription process where a new subscriber must confirm their email address by clicking a link in a confirmation email before being added to your list. This improves list quality and is recommended for GDPR compliance.

Drip Campaign

A series of pre-written emails sent automatically on a schedule after a subscriber joins a list or takes a specific action. Common examples include welcome sequences and onboarding flows.

E

Engagement Rate

A combined measure of how subscribers interact with your emails - typically including opens, clicks, and forwards. High engagement signals to inbox providers that your emails are wanted and relevant.

ESP (Email Service Provider)

A platform or service used to create, send, and track email campaigns. Examples include Pigeon, Mailchimp, and MailerLite.

H

Hard Bounce

A permanent delivery failure caused by an invalid, non-existent, or blocked email address. Hard bounced addresses should be removed from your list immediately to protect your sender reputation.

I

IP Warming

The gradual process of increasing email sending volume from a new IP address to build a positive sender reputation with inbox providers. Sending too much too fast from a new IP can trigger spam filters.

L

List Hygiene

The practice of regularly removing invalid, inactive, or unengaged subscribers from your email list. A clean list improves deliverability, open rates, and reduces costs.

List Segmentation

Dividing your email list into smaller groups based on shared characteristics or behaviors - such as location, engagement level, or purchase history - to send more relevant, targeted campaigns.

O

Open Rate

The percentage of delivered emails that were opened by recipients. Open rates vary significantly by industry but a 20-30% open rate is generally considered healthy for most small business newsletters.

Opt-in

The act of a subscriber giving explicit permission to receive emails from you. Single opt-in adds them immediately; double opt-in requires a confirmation click.

Opt-out

The process of a subscriber removing themselves from your email list, typically by clicking an unsubscribe link. Honoring opt-outs promptly is legally required in most countries.

P

Preheader

The short preview text that appears next to or below the subject line in most email clients. A well-written preheader complements the subject line and encourages opens.

S

Sender Reputation

A score assigned by inbox providers based on your sending history, bounce rate, complaint rate, and engagement. A poor sender reputation causes emails to land in spam.

Soft Bounce

A temporary email delivery failure caused by issues like a full inbox or a temporarily unavailable server. Unlike hard bounces, soft bounces may resolve on their own, but repeated soft bounces to the same address should be treated as permanent.

SPF (Sender Policy Framework)

A DNS record that lists which mail servers are authorized to send email on behalf of your domain. SPF helps inbox providers verify that your emails are legitimate.

Subject Line

The first line of text a recipient sees when your email arrives in their inbox. A compelling subject line is one of the most important factors in whether subscribers open your email.

Suppression List

A list of email addresses that should never receive emails from you - typically including hard bounces, spam complainants, and manual unsubscribes. Maintaining a suppression list protects your sender reputation.

T

Transactional Email

An automated email triggered by a specific user action - such as a purchase confirmation, password reset, or account notification. Unlike marketing emails, transactional emails are sent one-to-one rather than to a list.

U

Unsubscribe Rate

The percentage of recipients who opted out of your list after receiving a campaign. A healthy unsubscribe rate is generally below 0.5%. Higher rates may signal irrelevant content or too-frequent sending.

W

Welcome Email

The first email a new subscriber receives after joining your list. Welcome emails typically have the highest open rates of any campaign type and set the tone for the subscriber relationship.