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Glossary

Email marketing glossary

80 terms, from A/B test to webhook — explained in plain English.

A

Abandoned-cart email
An automated email sent to a shopper who added items to their cart but didn’t complete the purchase. It is often a short series of reminders sent over a day or two. Read moreSee also: Automation, Drip campaign
A/B test
Sending two or more versions of an email to small samples of your list to see which performs better, then sending the winner to everyone else. You can test the subject line, sender name, content or send time. Read moreSee also: Open rate, Click-through rate (CTR)
Apple Mail Privacy Protection (MPP)
A privacy feature Apple introduced in 2021 that pre-loads email content, including tracking images, for Apple Mail users who turn it on. Many emails therefore register as opened whether or not they were read, which makes open rates less reliable. Read moreSee also: Open rate, Tracking pixel, Click-to-open rate (CTOR)
Automation
A sequence of emails and actions that runs on its own when a trigger happens, such as a sign-up, purchase or birthday. Automations can include waits, conditions, branches and goals. Read moreSee also: Drip campaign, Welcome series, Webhook

B

BIMI
Brand Indicators for Message Identification: a standard that lets supporting mailbox providers show your logo beside authenticated emails. It requires a DMARC policy of quarantine or reject, and providers such as Gmail also require a mark certificate. Read moreSee also: DMARC, Sender reputation
Blocklist
A list of IP addresses or domains known for sending spam, used by mailbox providers and filters to block or filter mail. Listings usually follow spam-trap hits or high complaint rates. Read moreSee also: Spam trap, Sender reputation
Bounce rate
The percentage of emails that couldn’t be delivered, counting both hard and soft bounces. A consistently high bounce rate points to a poorly maintained list and harms your reputation. Read moreSee also: Hard bounce, Soft bounce, List hygiene
Bulk sender
Under Gmail’s rules, a sender that has sent close to 5,000 or more messages in a day to personal Gmail accounts. Bulk senders must meet extra requirements, including DMARC, one-click unsubscribe and a low spam rate; Yahoo applies similar rules. Read moreSee also: DMARC, RFC 8058 one-click unsubscribe, Complaint rate

C

CAN-SPAM Act
The US law governing commercial email. It requires honest headers and subject lines, identification of the message as an advertisement, a valid physical postal address and a working opt-out honoured within 10 business days. Read moreSee also: GDPR, CASL, Opt-out
CASL
Canada’s Anti-Spam Legislation. It generally requires consent before sending commercial electronic messages, along with clear sender identification and an unsubscribe mechanism. Read moreSee also: CAN-SPAM Act, Consent
Click-through rate (CTR)
The percentage of delivered emails in which at least one link was clicked. It is a more dependable measure of engagement than open rate. Read moreSee also: Click-to-open rate (CTOR), Open rate
Click-to-open rate (CTOR)
Unique clicks divided by unique opens. It shows how compelling the content was to people who opened, though inflated opens from privacy features can distort it. Read moreSee also: Click-through rate (CTR), Apple Mail Privacy Protection (MPP)
CNAME record
A DNS record that points one domain name at another. Email platforms often use CNAME records for DKIM keys and branded tracking domains. Read moreSee also: DKIM, Tracking domain, DNS
Complaint rate
The share of recipients who mark your email as spam. Gmail and Yahoo expect bulk senders to stay below 0.3%, and around 0.1% or lower is a healthier target. Read moreSee also: Feedback loop, Bulk sender, Sender reputation
Conversion rate
The percentage of recipients who complete a goal after an email, such as buying or registering. Measuring it usually needs revenue tracking or UTM parameters. Read moreSee also: UTM parameters, Click-through rate (CTR)

D

Data fiduciary
Under the DPDP Act, the person or business that decides why and how personal data is processed. A company running email marketing is the data fiduciary for its subscriber list. Read moreSee also: Data principal, Data processor, DPDP Act
Data principal
Under the DPDP Act, the individual the personal data relates to; for an email list, the subscriber. For a child, it includes their parent or lawful guardian. Read moreSee also: Data fiduciary, DPDP Act
Data processor
A business that processes personal data on behalf of another, such as an email platform handling a customer’s list. The data fiduciary (or controller, under GDPR) remains responsible for compliance. Read moreSee also: Data fiduciary, GDPR
Dedicated IP
An IP address used by only one sender, so its reputation depends entirely on that sender’s practices. It suits consistent high volume and must be warmed up before full use. Read moreSee also: Shared IP, IP warm-up, Sender reputation
Deliverability
The ability of your emails to reach recipients’ inboxes rather than being filtered to spam or rejected. It depends on authentication, sender reputation, list quality and engagement. Read moreSee also: Inbox placement, Sender reputation, SPF
DKIM
DomainKeys Identified Mail: a digital signature added to each email and checked against a public key published in your DNS. It proves the message came from your domain and wasn’t altered in transit. Read moreSee also: SPF, DMARC, CNAME record
DMARC
Domain-based Message Authentication, Reporting and Conformance: a DNS policy that tells receivers what to do with mail that fails aligned SPF and DKIM checks (none, quarantine or reject) and where to send reports. Gmail and Yahoo require bulk senders to publish one. Read moreSee also: SPF, DKIM, BIMI, Bulk sender
DNS
The Domain Name System, which holds the records for your domain, such as where your website and mail live. Email authentication records (SPF, DKIM and DMARC) are published in DNS. Read moreSee also: SPF, DKIM, DMARC, CNAME record
Domain warm-up
Building sending volume gradually on a new or long-unused sending domain, starting with your most engaged contacts. It follows the same idea as IP warm-up, because mailbox providers track domain reputation too. Read moreSee also: IP warm-up, Sender reputation
Double opt-in
A sign-up process in which the person must click a link in a confirmation email before being added to your list. It keeps out typos, fake addresses and spam traps, and gives strong proof of consent. Read moreSee also: Single opt-in, Opt-in, Consent record
DPDP Act
India’s Digital Personal Data Protection Act, 2023, which governs how digital personal data is processed. Its Rules were notified in November 2025 and are being brought into force in phases. Read moreSee also: Consent, Data fiduciary, Data principal, Consent manager
Drip campaign
A pre-written series of emails sent automatically on a schedule after a trigger such as a sign-up. More advanced automations add branches based on behaviour. Read moreSee also: Automation, Welcome series
Dynamic content
Parts of an email that change depending on who receives it, based on fields, tags or behaviour, such as a different product block for each city. It lets one email serve several segments. Read moreSee also: Merge tag, List segmentation

E

Email service provider (ESP)
A platform that sends email on your behalf and provides tools for managing lists, designing emails, automating journeys and reporting. Read moreSee also: Deliverability, Transactional email
Engagement
How recipients interact with your emails: opening, clicking, replying and forwarding, or deleting unread and marking as spam. Mailbox providers rely heavily on engagement when deciding where to place mail. Read moreSee also: Open rate, Click-through rate (CTR), Re-engagement campaign

F

Feedback loop
A service from a mailbox provider that reports when its users mark your email as spam, so you can unsubscribe them. Some providers report individual complaints; Gmail provides aggregate data instead. Read moreSee also: Complaint rate, Suppression list

G

GDPR
The EU General Data Protection Regulation, which governs the personal data of people in the European Union. For marketing email it generally requires a lawful basis, usually consent, and gives people rights to access, correct and erase their data. Read moreSee also: Consent, CAN-SPAM Act, DPDP Act

H

Hard bounce
A permanent delivery failure, for example because the address or domain doesn’t exist. Hard-bounced addresses should be suppressed immediately. Read moreSee also: Soft bounce, Bounce rate, Suppression list

I

Inbox placement
The percentage of emails that land in the inbox rather than spam, measured with seed tests or panel data. Unlike delivery rate, it shows where accepted mail actually ended up. Read moreSee also: Deliverability, Seed list
IP warm-up
Gradually increasing the volume sent from a new IP address so mailbox providers can build a reputation for it. Sending large volumes from a cold IP often leads to throttling or spam filtering. Read moreSee also: Domain warm-up, Dedicated IP, Throttling

L

Landing page
A standalone web page with a single purpose, such as collecting sign-ups for a lead magnet or registrations for an event. Read moreSee also: Lead magnet, Opt-in
Lead magnet
Something valuable offered in exchange for an email address, such as a guide, checklist, discount or free trial. Read moreSee also: Landing page, Welcome series
List hygiene
Routine cleaning of your list: removing bounces, suppressing complainers, and re-engaging or removing inactive contacts. Good hygiene protects your reputation and lowers your costs. Read moreSee also: Hard bounce, Re-engagement campaign, Spam trap, Sunset policy
List segmentation
Dividing your contacts into groups based on fields, tags, behaviour or purchases so you can send more relevant emails. Dynamic segments update automatically as the data changes. Read moreSee also: Dynamic content, Tag
List-Unsubscribe header
An email header that gives mailbox providers a standard way to show an unsubscribe option next to your sender name. Combined with the List-Unsubscribe-Post header, it enables one-click unsubscribe. Read moreSee also: RFC 8058 one-click unsubscribe, Opt-out

M

Merge tag
A placeholder such as {{first_name}} that is replaced with each contact’s own data when an email is sent. A fallback value avoids blanks when the field is empty. Read moreSee also: Dynamic content, Spintax

O

Open rate
The percentage of delivered emails recorded as opened, based on a tracking image loading. Since Apple Mail Privacy Protection it overstates real opens, so it is best used to spot trends rather than as an exact figure. Read moreSee also: Apple Mail Privacy Protection (MPP), Tracking pixel, Click-through rate (CTR)
Opt-in
Actively agreeing to receive emails, for example by ticking an unticked box or submitting a sign-up form. Read moreSee also: Double opt-in, Single opt-in, Consent
Opt-out
Choosing to stop receiving emails, usually by unsubscribing. The term also describes adding people by default and making them ask to be removed, which laws such as GDPR and the DPDP Act do not treat as valid consent. Read moreSee also: Opt-in, Suppression list, Unsubscribe rate

P

Pop-up form
A sign-up form that appears over a web page, triggered by time on page, scroll depth or an attempt to leave. Used with restraint, it is one of the most effective ways to grow a list. Read moreSee also: Landing page, Lead magnet, Opt-in
Postmaster Tools
Free dashboards from mailbox providers, notably Google Postmaster Tools, that show your domain’s spam rate, authentication results and compliance with sender requirements. Read moreSee also: Complaint rate, Sender reputation
Preference centre
A page where subscribers choose which emails they receive and how often, or update their details. It gives people an alternative to unsubscribing from everything. Read moreSee also: Opt-out, Consent
Preheader
The short preview text shown after the subject line in most inboxes. Writing it deliberately adds context and can lift opens. Read moreSee also: Open rate, A/B test
PTR record
A reverse DNS record that maps an IP address back to a hostname. Mailbox providers expect sending IPs to have valid forward and reverse DNS. Read moreSee also: DNS, Dedicated IP

R

Re-engagement campaign
Emails sent to contacts who haven’t opened or clicked for a while, asking whether they still want to hear from you. Those who don’t respond are usually removed or suppressed. Read moreSee also: List hygiene, Engagement, Sunset policy
Resend to non-openers
Sending a campaign again, often with a new subject line, to people who didn’t open it the first time. Use it sparingly, as repeated sends can raise complaints. Read moreSee also: Open rate, A/B test
Return-Path
The address that bounce messages are sent to, also called the envelope sender. For SPF to count towards DMARC, its domain must align with your From domain, for example bounces.yourbrand.com for yourbrand.com. Read moreSee also: SPF, DMARC
RFC 8058 one-click unsubscribe
The technical standard that lets a mailbox provider unsubscribe someone with a single click, using the List-Unsubscribe and List-Unsubscribe-Post headers, without visiting a web page. Gmail and Yahoo require it for bulk marketing mail. Read moreSee also: List-Unsubscribe header, Bulk sender
RSS-to-email
Automatically turning new posts from a blog or website feed into email, either one email per post or as a regular digest. Read moreSee also: Automation

S

Seed list
A set of test addresses across different mailbox providers, used to check where an email lands (inbox, promotions or spam) before or during a send. Read moreSee also: Inbox placement
Sender name
The name shown in the inbox as who the email is from. A consistent, recognisable sender name is one of the biggest influences on whether people open. Read moreSee also: Open rate, A/B test
Sender reputation
The trust mailbox providers place in your sending domain and IP addresses, based on authentication, bounces, complaints, spam-trap hits and engagement. It is the main factor in inbox placement. Read moreSee also: Sender Score, Deliverability, Complaint rate
Sender Score
A reputation score from 0 to 100 for an IP address, published by Validity. It is a useful indicator, though each mailbox provider relies on its own internal reputation data. Read moreSee also: Sender reputation
Send-time optimisation
Delivering an email to each contact at the time they are most likely to engage, based on their past behaviour. Read moreSee also: Time-zone sending, Engagement
Shared IP
An IP address used by many senders on the same platform. Its reputation is pooled, which suits lower or irregular volumes on a well-managed platform. Read moreSee also: Dedicated IP, Sender reputation
Single opt-in
A sign-up process in which the address is added straight away, without a confirmation email. It is quicker, but more exposed to typos, fake sign-ups and spam traps. Read moreSee also: Double opt-in, Opt-in
Soft bounce
A temporary delivery failure, for example a full mailbox or a server that is briefly unavailable. Addresses that soft-bounce repeatedly should be suppressed. Read moreSee also: Hard bounce, Bounce rate
Spam trap
An address used by mailbox providers or blocklist operators to catch senders with poor list practices. Hitting traps, which is common with bought or very old lists, can get you blocklisted. Read moreSee also: Blocklist, List hygiene, Double opt-in
SPF
Sender Policy Framework: a DNS TXT record listing the servers allowed to send email for your domain. Receivers check it to spot forged senders. Read moreSee also: DKIM, DMARC, Return-Path
Spintax
Syntax that picks one of several alternatives for each recipient, written in MailNesto as {{spin:Hello|Hi|Hey}}. It adds natural variation to wording across a send. Read moreSee also: Merge tag, Dynamic content
Sunset policy
A rule for when to stop emailing contacts who haven’t engaged for a set period, such as six months, usually after a final re-engagement attempt. Read moreSee also: Re-engagement campaign, List hygiene
Suppression list
A list of addresses that must never receive marketing email: unsubscribes, hard bounces, complainers and manual blocks. It should apply to every send and every import. Read moreSee also: Opt-out, Hard bounce, Feedback loop

T

Tag
A label attached to a contact to record an interest, source or action. Tags are used to build segments and to trigger automations. Read moreSee also: List segmentation, Automation
Throttling
When a mailbox provider temporarily slows down or defers accepting your mail, often because volume rose suddenly or reputation dropped. Sending platforms respond by slowing down and retrying. Read moreSee also: IP warm-up, Soft bounce
Time-zone sending
Scheduling a campaign to arrive at the same local time for every subscriber, based on each contact’s time zone. Read moreSee also: Send-time optimisation
Tracking domain
The domain used in tracked links and open-tracking images. A branded tracking domain uses your own domain, which looks more trustworthy and keeps your link reputation separate from other senders. Read moreSee also: CNAME record, Sender reputation
Tracking pixel
A tiny, invisible image in an email; when it loads, an open is recorded. Image blocking and privacy features make it an imperfect signal. Read moreSee also: Open rate, Apple Mail Privacy Protection (MPP)
Transactional email
A one-to-one message triggered by something the recipient did, such as an order receipt, password reset or OTP. It is expected by the recipient and is usually sent separately from marketing email. Read moreSee also: Email service provider (ESP), Webhook

U

Unsubscribe rate
The percentage of recipients who unsubscribe after a campaign. A small number is normal; a spike suggests a mismatch between what people expected and what you sent, or how often. Read moreSee also: Opt-out, Preference centre, Complaint rate
UTM parameters
Tags added to links, such as utm_source=email, so analytics tools can attribute website visits and sales to a specific campaign. Read moreSee also: Conversion rate, Click-through rate (CTR)

W

Webhook
An automatic HTTP request sent to another system when an event happens, such as a subscribe, bounce or click. Webhooks keep your CRM, store or database in sync in real time. Read moreSee also: Automation, Transactional email
Welcome series
A short sequence of automated emails sent to new subscribers to introduce your brand and deliver anything promised at sign-up. It typically has three or four emails over a week or two. Read moreSee also: Drip campaign, Automation, Lead magnet