45 email marketing terms, explained in plain English.
A
- A/B test
- Sending two versions of an email (for example, different subject lines) to parts of your list to see which performs better. Test one variable at a time for clear results.
- Autoresponder
- An email sent automatically in response to an action, such as a new signup. A series of them is often called an autoresponder sequence.
B
- BIMI
- Brand Indicators for Message Identification, a standard that can display your brand logo next to your emails in supporting inboxes. It requires DMARC at an enforcement policy, and some providers also require a verified mark certificate.
- Bounce (hard/soft)
- An email that couldn't be delivered. A hard bounce is permanent (like a nonexistent address) and should be removed; a soft bounce is temporary (like a full inbox) and may succeed later.
C
- CAN-SPAM
- The US law governing commercial email. It requires accurate headers, a non-deceptive subject, a valid physical postal address and a working opt-out honored promptly. Not legal advice.
- CASL
- Canada's Anti-Spam Legislation, which generally requires consent (express or, in limited cases, implied) before sending commercial messages, plus sender identification and an unsubscribe option. Not legal advice.
- Click-to-open rate
- The share of people who opened an email and then clicked a link (unique clicks divided by unique opens). Because Apple Mail Privacy Protection inflates opens, treat it with caution.
- Co-registration
- A list-building method where people sign up for your emails while signing up for someone else's offer, usually via a checkbox. Subscriber quality varies, so use it carefully.
- Cold list
- A list of people who haven't engaged recently or never opted in to hear from you. Sending to purchased or scraped cold lists risks spam complaints and spam traps.
- Complaint rate
- The percentage of recipients who mark your email as spam. Gmail and Yahoo expect bulk senders to stay below 0.3%, and aiming for under 0.1% is safer.
- CTR
- Click-through rate: the share of delivered emails that received at least one click. It's generally a more trustworthy engagement metric than open rate.
- Custom field
- A data field you add to subscriber profiles beyond the basics, like birthday, interest or plan type. Custom fields power personalization and segmentation.
D
- Deliverability
- Your ability to get emails into recipients' inboxes rather than spam folders or blocks. It depends on authentication, sender reputation, list quality and engagement.
- DKIM
- DomainKeys Identified Mail, an authentication method that adds a cryptographic signature to your emails. Receiving servers check it against a public key in your DNS to verify the message wasn't altered.
- DMARC
- Domain-based Message Authentication, Reporting and Conformance, a DNS policy that tells receivers what to do when SPF or DKIM checks fail to align with your From domain. It also enables reports about who is sending as your domain.
- Double opt-in
- A signup process where new subscribers must confirm their address by clicking a link in a confirmation email. It reduces typos, bots and spam traps.
- Drip campaign
- A series of pre-written emails sent automatically on a schedule or based on triggers. Welcome sequences and onboarding courses are common examples.
E
- Engagement
- How subscribers interact with your emails through opens, clicks, replies and forwards. Mailbox providers use engagement signals when deciding inbox placement.
- ESP
- Email Service Provider, the platform you use to manage your list and send campaigns. Examples include Kit, Beehiiv, MailerLite, Mailchimp and Brevo.
G
- GDPR
- The EU's General Data Protection Regulation, which governs personal data of people in the EU. For email marketing it generally means having a lawful basis such as clear, freely given consent and honoring data rights. Not legal advice.
H
- Hygiene
- The ongoing practice of cleaning your list by removing bounces, invalid addresses and long-term inactive subscribers. Good hygiene protects deliverability.
I
- IP warm-up
- Gradually increasing sending volume from a new IP address so mailbox providers can build trust in it. Start with your most engaged subscribers.
L
- Lead magnet
- A free resource, like a checklist, template or mini-course, offered in exchange for an email address. The best ones solve a specific problem fast.
- List-Unsubscribe header
- An email header that lets mailbox providers display a built-in unsubscribe button. Gmail and Yahoo expect bulk senders to support one-click unsubscribe via this header.
M
- Merge tag
- A placeholder in an email, like a first-name field, that your ESP replaces with each subscriber's data when sending. Always set a fallback value.
- MPP (Apple Mail Privacy Protection)
- An Apple Mail feature that can preload email content, including tracking pixels, which registers opens whether or not the person read the email. It inflates open rates.
O
- Open rate
- The percentage of delivered emails recorded as opened, typically tracked with an invisible pixel. Privacy features and image blocking make it an imprecise metric.
P
- Plain-text email
- An email with no HTML formatting, or one designed to look simple and personal. Plain-text-style emails often feel more like a one-to-one message.
- Preheader
- The short preview text shown after the subject line in many inboxes. Use it to add context or curiosity rather than leaving it to default text.
R
- Reputation
- The trust score mailbox providers assign to your sending domain and IP based on complaints, bounces, engagement and authentication. Good reputation means better inbox placement.
- RPS (revenue per subscriber)
- Total email-attributed revenue divided by the number of subscribers over a period. It shows what your list is really worth.
S
- Seed list
- A set of test email addresses across different mailbox providers used to check inbox placement and rendering before or during a send.
- Segmentation
- Dividing your list into groups based on data like interests, behavior or purchase history. Segmented sends are usually more relevant and perform better.
- Sender score
- A reputation rating, often on a 0-100 scale, estimating how trustworthy a sending IP is. Various providers calculate their own versions.
- Soft opt-in
- In some jurisdictions, a basis for emailing existing customers about similar products without fresh explicit consent, as long as they could opt out when giving their details and in every message. Rules vary by country. Not legal advice.
- Spam trap
- An email address used by mailbox providers or blocklist operators to catch senders with poor list practices. Hitting one can badly hurt your reputation.
- SPF
- Sender Policy Framework, a DNS record listing the servers allowed to send email for your domain. Receiving servers use it to spot forged senders.
- Sunset policy
- A rule for removing or suppressing subscribers who haven't engaged over a set period, usually after a re-engagement attempt. It keeps your list healthy.
- Suppression list
- A list of addresses your ESP will never send to, such as unsubscribes, hard bounces and complainers. It prevents accidental re-mailing.
T
- Tag
- A label attached to a subscriber, often based on actions like clicks or purchases. Tags make it easy to segment and trigger automations.
- Transactional email
- A one-to-one message triggered by a user action, like a receipt, password reset or shipping notice. These generally have different rules than marketing emails.
- Trigger
- The event that starts an automation, such as signing up, clicking a link, making a purchase or reaching a date.
U
- Unsubscribe rate
- The percentage of recipients who opt out after a send. Some unsubscribes are healthy; a sudden spike signals a content or frequency problem.
W
- Welcome sequence
- The series of emails a new subscriber receives right after signing up. It sets expectations, delivers value and often drives first sales.
- Whitelist/Safelist
- Adding a sender to your contacts or approved list so their emails are more likely to reach your inbox. Many senders ask new subscribers to do this.