Measurement / CTR
Click-through rate
The percentage of delivered messages that produced at least one tracked link click.
Email field guide
Know the terms.
Understand the system.
23 IN-DEPTH DEFINITIONS
Email language, explained in context. Learn how each concept works, why it matters, what teams get wrong, and which terms connect next.
View glossary as Markdown/
All definitions23
C
D
Authentication / DMARC
Domain-based Message Authentication, Reporting, and Conformance
An alignment, policy, and reporting layer that connects SPF or DKIM to the visible From domain.
Authentication / DKIM
DomainKeys Identified Mail
A cryptographic signature that lets a domain take responsibility for selected message content.
Audience
Double opt-in
A subscription process that requires a person to confirm control of the submitted email address.
E
Authentication
Email authentication
The DNS and cryptographic mechanisms receivers use to verify sending identities and domain authorization.
Automation
Email automation
A system that sends or changes email journeys in response to time, customer state, or events.
Deliverability / DNSBL / RBL
Email blocklist
A published or private dataset of IPs or domains associated with unwanted or risky email.
Deliverability
Email deliverability
The ability to reach the part of the mailbox where a wanted recipient can find and act on an email.
Audience
Email segmentation
The practice of selecting recipients using shared attributes, consent, lifecycle state, or behavior.
Messaging
Email subject line
The brief message label that tells a recipient what an email is about before opening.
H
Deliverability
Hard bounce
A permanent delivery failure, commonly caused by an invalid address or a definitive policy rejection.
I
Deliverability
Inbox placement
Where accepted email is placed, such as the primary inbox, another inbox tab, spam, or junk.
Deliverability
IP reputation
The sending history and risk signals mailbox providers associate with an IP address.
L
Audience
List hygiene
The ongoing practice of keeping audience permission, reachability, source, and engagement data trustworthy.
O
Audience
One-click unsubscribe
A standards-based HTTPS mechanism that lets a mailbox provider submit an unsubscribe request without a login or confirmation page.
Measurement
Open rate
The share of delivered messages for which the sender recorded at least one tracking-pixel load.
S
Messaging
Sender name
The display name shown beside an email address to identify the person, brand, or team sending.
Authentication / SPF
Sender Policy Framework
A DNS policy that authorizes IP addresses to use a domain in the SMTP envelope.
Deliverability
Sender reputation
A receiver-specific assessment of sending identity and behavior used when filtering email.
Deliverability
Soft bounce
A temporary delivery failure that may succeed when retried under a controlled policy.
Deliverability
Spam complaint
A recipient signal that a message is unwanted, usually created by marking it as spam or junk.
Audience
Suppression list
A durable do-not-send control containing recipients or destinations that must not receive certain email.
T
Automation
Transactional email
A message triggered by an individual action, account event, or existing transaction.
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