Key terms and concepts related to email deliverability, authentication, and reputation management. Use this reference to understand the terminology used across Blueshift's deliverability documentation.
A/B Testing #
Comparing two versions of an email to determine which performs better.
Subject line A/B testing, content A/B testing.
Authenticated Received Chain ARC #
A protocol that preserves email authentication results as messages pass through multiple intermediary servers.
ARC-Message-Signature #
A cryptographic signature within the ARC framework that validates the original message headers and body, ensuring content has not been altered during relay or forwarding.
Authenticated Received Chain Seal ARC-Seal #
A cryptographic signature added by each intermediary mail server to record the authentication status (SPF, DKIM, DMARC) it observed, preserving trust in authentication results when emails are forwarded or relayed.
Barracuda #
A security organization that provides spam filtering and blocklisting services to prevent malicious or unwanted emails.
Brand Indicators for Message Identification BIMI #
A standard that displays a brand's verified logo alongside authenticated emails in the recipient's inbox.
Blocklist #
A list of IP addresses or domains known for sending spam or unwanted emails, used by ISPs and mailbox providers to filter incoming mail.
Blocklisting #
The act of adding a sender's IP address or domain to a blocklist due to suspicious or abusive sending activity.
Blocks #
When a receiving mail server actively prevents emails from being delivered, typically due to sender reputation or policy violations.
Bot Clicks #
Automated clicks generated by security filters or anti-spam systems rather than real user interactions.
Bounce #
An email that could not be delivered to the recipient's mailbox.
Campaign #
A batch of emails sent to a specific audience for a marketing or transactional goal.
CAN-SPAM Act #
A U.S. law that sets rules for commercial email and gives recipients the right to opt out of future messages.
Clicks #
The number of times recipients click links within an email.
Compliance #
Adhering to the legal, technical, and ethical standards that govern email marketing.
Content Filter #
A system that analyzes email content to detect spammy language, formatting, or structural elements.
Click-Through Rate CTR #
The percentage of recipients who clicked at least one link in an email, calculated as clicks divided by opens.
Custom Header #
A user-defined email header (for example, X-Campaign-ID or X-Mailer) added to a message for tracking, identification, or diagnostic purposes beyond standard headers.
Domain Alignment Result Attribute DARA #
A Gmail-specific header attribute indicating the domain Gmail considers aligned during ARC or DMARC authentication.
Dedicated IP #
An IP address used exclusively by a single sender for email delivery.
Deliverability Audit #
A comprehensive review of technical setup, sender reputation, and email performance to identify delivery issues.
Deliverability Monitoring #
Continuous tracking of delivery metrics and sender reputation to detect and resolve issues proactively.
DomainKeys Identified Mail DKIM #
An authentication method that uses cryptographic signatures to confirm an email's integrity and verify it has not been tampered with in transit.
Domain-based Message Authentication, Reporting & Conformance DMARC #
An email authentication policy that builds on SPF and DKIM, enabling domain owners to specify how unauthenticated messages should be handled and to receive aggregate reports.
Domain Name System DNS #
The system that translates domain names into IP addresses and stores key email-related records such as MX, SPF, and DKIM.
DNS-based Blocklist DNSBL #
A DNS-hosted list of IP addresses or domains known for sending spam or malicious email.
Domain Alignment #
When the domain in SPF or DKIM authentication matches the domain in the "From" header, as required by DMARC.
Double Opt-in #
A subscription process that requires the user to confirm their email address before being added to a mailing list.
Email Authentication #
The process of verifying the legitimacy of an email sender using protocols like SPF, DKIM, and DMARC.
Email Body #
The main content section of an email message.
Email Fatigue #
Recipient disengagement caused by receiving too many or overly repetitive emails.
Email Header #
The section of an email containing metadata such as sender, recipient, timestamps, and authentication results.
Email Service Provider (ESP) #
A platform that enables businesses to send, track, and manage email campaigns.
Email Spoofing #
Forging the sender address to make an email appear to come from a trusted source.
Engagement #
The level of interaction recipients have with emails, measured through opens, clicks, and replies.
Envelope From #
The return-path domain used for bounce handling and SPF checks.
Forward DNS FDNS #
The process of resolving a domain name to its corresponding IP address.
Feedback Loop (FBL) #
A system through which ISPs report spam complaints back to the sender or ESP.
General Data Protection Regulation GDPR #
An EU regulation governing data privacy and requiring explicit consent for processing personal data.
Google Postmaster Tools (GPT) #
Google's reporting interface that provides data on domain reputation, spam rates, and authentication results for senders.
Google Site Verification #
A process of verifying domain ownership for Google services such as Postmaster Tools.
Greylisting #
A temporary rejection tactic where emails from unknown senders are initially deferred, expecting legitimate servers to retry.
Hard Bounce #
A permanent delivery failure caused by an invalid, non-existent, or blocked recipient address.
HTML Email #
An email format that supports rich elements such as images, links, and styled text.
Image-to-Text Ratio #
The proportion of images versus text in an email, which affects spam filter scoring. The recommended ratio is 60% text to 40% images.
Inactive Subscribers #
Recipients who have not engaged with emails over a defined period.
Inbox Monitoring #
Testing whether emails land in the inbox, spam folder, or other locations.
IP Warmup #
The practice of gradually increasing send volume from a new IP address to build a positive sending reputation.
Internet Service Provider ISP #
A company that provides internet access and hosts users' email inboxes (for example, Gmail, Yahoo).
Link Tracking Domain #
A domain used to track link clicks within an email for analytics purposes.
List #
A collection of email addresses used for sending campaigns.
List-Unsubscribe #
An email header that provides recipients with a standardized way to opt out of future emails, typically through a mailto link or a one-click HTTPS URL recognized by major mailbox providers.
Mailbox Provider #
The service that hosts the recipient's email inbox (for example, Gmail, Outlook.com).
Message-ID #
A unique identifier automatically assigned to each email message.
MIME-Version #
An email header indicating the version of the MIME protocol used, enabling messages to include multiple content types such as text, HTML, attachments, and multimedia.
MX Record #
A DNS record that specifies which mail servers are responsible for receiving email on behalf of a domain.
Opens #
The number of times recipients open an email, typically tracked using an invisible tracking pixel.
Personalization #
Using recipient-specific data (such as name, behavior, or preferences) to tailor email content.
Phishing #
Fraudulent attempts to obtain sensitive information through deceptive emails that mimic trusted sources.
Plain Text Email #
An email containing only unformatted text with no HTML elements.
Postmaster #
The administrator responsible for managing email delivery, authentication, and domain reputation for an organization.
Postmaster Tools #
Platforms (such as Google Postmaster Tools or Microsoft SNDS) that provide reputation and deliverability insights for senders.
Pre-fetch Open #
An open event generated automatically when an email client preloads images, not representing actual user engagement.
Pre-header Text #
The preview snippet displayed beside or below the subject line in the inbox.
Pristine Spam Trap #
An email address that was never used by a real person, created specifically to catch senders who harvest addresses.
Proxy Open #
An open event triggered when a proxy server (such as Apple Mail Privacy Protection) fetches images on the user's behalf.
PTR Record #
A DNS record that maps an IP address back to a domain name through reverse DNS lookup.
Rate Limit #
The maximum number of emails a sender can deliver to a specific domain within a given time frame.
Reverse DNS RDNS #
A lookup process that verifies whether an IP address resolves to a valid, matching domain name.
Re-engagement Campaign #
A targeted campaign designed to reactivate subscribers who have become inactive.
Received-SPF #
An email header added by the receiving mail server showing the result of the SPF check (for example, pass, fail, or softfail).
Recycled Spam Trap #
A formerly active email address that has been repurposed to identify senders who continue emailing inactive or abandoned addresses.
Rendering #
How an email visually appears across different devices and email clients.
Return Path #
The email address designated to receive bounce notifications.
Seed List #
A set of monitored test email addresses used to check inbox placement across different mailbox providers.
Seed Test #
The process of sending test emails to a seed list to evaluate inbox deliverability before a full campaign send.
Segment #
A group of subscribers filtered by specific behaviors or attributes for more targeted email sends.
Sending Domain #
The domain name used in the "From" address or return-path during email delivery.
Sending IP #
The IP address from which emails are sent to recipients.
Shared IP #
An IP address used by multiple senders for email delivery.
Smart Network Data Services SNDS #
Microsoft's reputation reporting system for senders to monitor the health and reputation of their sending IPs.
Soft Bounce #
A temporary delivery failure caused by conditions such as a full mailbox, server errors, or policy restrictions.
SORBS #
A blocklist system that maintains databases of known spam sources and open relays.
Spam #
Unsolicited or irrelevant email, typically sent in bulk.
Spam Filter #
A system that classifies incoming email as spam or legitimate based on content, sender reputation, and other signals.
Spam Keywords #
Words or phrases commonly flagged by spam filters, such as "free," "urgent," or "act now."
Spam Score #
A numerical value indicating how likely an email is to be classified as spam by filters.
Spam Trap #
An email address designed to identify spammers and senders with poor list hygiene practices.
Spamhaus #
A leading global blocklist provider that tracks and catalogs spammers and spam-related activity.
Sender Policy Framework SPF #
A DNS-based authentication method that verifies whether a sending mail server is authorized to send on behalf of a domain.
Subject Line #
The first visible line of text that summarizes or previews the email's content.
Subdomain #
A secondary domain under the main domain, often used to separate different email streams (for example, marketing.example.com).
Sunset Policy #
A rule for gradually removing inactive subscribers from mailing lists to maintain list hygiene and protect sender reputation.
Suppression List #
A list of email addresses excluded from sends to prevent errors, complaints, or legal issues.
Template #
A pre-designed email layout used for creating consistent messages across campaigns.
Throttling #
Controlling the rate of email sends to avoid overwhelming receiving servers or damaging sender reputation.
Transport Layer Security TLS Encryption #
A protocol that encrypts emails in transit between servers to protect data privacy.
Transactional Email #
Automated, behavior-triggered messages such as order confirmations, receipts, or password resets.
Typo Spam Trap #
A spam trap created using common domain misspellings (for example, gmial.com) to catch senders with unvalidated lists.
Unsubscribe #
The action taken by a recipient to opt out of receiving further emails from a sender.
User Open #
An open event triggered by a real user viewing the email, as opposed to bot or proxy opens.
Volume Ramp-up #
The process of gradually increasing email send volume to establish or maintain deliverability with mailbox providers.
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