Glossary
Email Marketing Glossary
30+ essential email marketing terms explained simply - from SMTP to DMARC.
SMTP
Simple Mail Transfer Protocol. The standard protocol for sending email between servers. Used by transactional email providers like Brevo, SendGrid and Postmark.
SPF
Sender Policy Framework. A DNS TXT record that lists which mail servers are authorized to send email from your domain.
DKIM
DomainKeys Identified Mail. A cryptographic signature added to outgoing email so receiving servers can verify the message was not tampered with.
DMARC
Domain-based Message Authentication, Reporting and Conformance. A policy that tells receiving servers what to do with email failing SPF or DKIM checks.
Bounce Rate
Percentage of sent emails that could not be delivered. Hard bounces are permanent failures, soft bounces are temporary.
Open Rate
Percentage of recipients who opened an email. Note: less reliable since Apple Mail Privacy Protection masks opens by default.
CTR
Click-Through Rate. Percentage of recipients who clicked at least one link in your email.
CTOR
Click-To-Open Rate. Clicks divided by opens. A purer engagement signal than CTR.
Deliverability
Whether your email reaches the inbox vs the spam folder. Influenced by sender reputation, content, authentication and engagement.
Sender Reputation
A score mailbox providers (Gmail, Outlook, Yahoo) assign to your sending domain and IP based on past behavior.
Warm-up
The process of gradually increasing sending volume from a new domain or IP to build sender reputation safely.
Transactional Email
Email triggered by a user action - password reset, receipt, verification. Distinct from marketing email.
Marketing Email
Promotional or informational email sent to a list, typically requires explicit consent (opt-in).
Double Opt-in
A subscription flow where a confirmation email is sent before adding the user to the list. Improves list quality.
List Segmentation
Splitting your subscriber list into groups based on attributes or behavior to send more relevant emails.
Drip Campaign
A sequence of pre-written emails sent on a schedule or triggered by user actions.
A/B Test
Sending two variants of an email to a small portion of your list to determine which performs better before sending to the rest.
Webhook
A real-time HTTP callback from your email provider to your app when events happen (delivered, opened, bounced).
API Key
A secret token used to authenticate requests to an email provider's API. Keep it server-side only.
Suppression List
A list of email addresses that should never be emailed - unsubscribes, bounces, complaints.
CAN-SPAM
US law governing commercial email. Requires accurate headers, identifying subject lines, postal address and an unsubscribe mechanism.
GDPR
EU regulation governing personal data including email. Requires explicit consent for marketing email.
Hard Bounce
A permanent delivery failure - invalid address, blocked domain. Should never be retried.
Soft Bounce
A temporary delivery failure - mailbox full, server down. Safe to retry.
Spam Trap
An email address used by ISPs and blocklists to identify senders with poor list hygiene.
Plain Text Email
An email with no HTML formatting. Often has better deliverability for transactional emails.
MTA
Mail Transfer Agent. The server software that actually sends and routes email (Postfix, Brevo's relay, etc.).
IP Reputation
How mailbox providers score the sending IP address based on past behavior.
Dedicated IP
An IP address used exclusively by one sender. Recommended for high-volume sending.