Email tracking and deliverability glossary
Definitions of the technical, regulatory, and metric terms that show up in B2B email tracking and deliverability decisions. Each entry includes a quick definition, detailed explanation, related terms, and FAQs.
Apple Mail Privacy Protection
Apple MPP, Mail Privacy Protection, MPP
Apple Mail Privacy Protection (MPP) is a privacy feature that launched with iOS 15 in September 2021.
Email Tracking Pixel
Tracking pixel, Web beacon, 1x1 pixel
An email tracking pixel is a 1x1 transparent image embedded in an email that loads from a tracker server when the recipient's mail client renders the message.
Email Open Rate
Open rate, Email opens, Open percentage
Email open rate is the percentage of email recipients whose mail client loaded the tracking pixel embedded in the message.
Gmail Image Proxy
googleusercontent.com, Gmail image cache
Gmail's image proxy is the system Google uses to route every embedded image in incoming Gmail messages through googleusercontent.
Email Deliverability
Deliverability, Inbox placement, Email delivery rate
Email deliverability is the rate at which sent emails reach the recipient's inbox rather than spam folder or being blocked entirely.
SPF, DKIM, and DMARC
Email authentication, SPF record, DKIM signature
SPF (Sender Policy Framework), DKIM (DomainKeys Identified Mail), and DMARC (Domain-based Message Authentication, Reporting & Conformance) are the three email authentication standards published as DNS records on the sender domain.
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Sender Reputation
Domain reputation, IP reputation, Sender score
Sender reputation is the score that mail providers (Gmail, Microsoft 365, Yahoo) assign to your sending domain and IP based on historical behaviour: bounce rate, spam-complaint rate, recipient engagement (opens, clicks, replies, deletes-without-reading), and consistency over time.
Email Warm-up
Sender warm-up, Inbox warm-up, Domain warm-up
Email warm-up is the practice of gradually ramping email volume from a new sending domain or IP to build positive sender reputation with mail providers.
Cold Email
Cold outreach, Outbound email
Cold email is outbound email sent to a recipient who has not opted in to receive email from the sender.
Email Bounce Rate
Bounce rate, Hard bounce, Soft bounce
Email bounce rate is the percentage of sent emails that fail to deliver to the recipient's mailbox.
SPF Record
Sender Policy Framework, SPF DNS record
SPF (Sender Policy Framework) is a DNS TXT record published on a sending domain that lists the IP addresses and hostnames authorised to send email for that domain.
DKIM Signature
DomainKeys Identified Mail, DKIM
DKIM is an email authentication standard that adds a cryptographic signature to each outbound message.
DMARC Policy
Domain-based Message Authentication, Reporting & Conformance
DMARC is a DNS TXT record at `_dmarc.
BIMI
Brand Indicators for Message Identification
BIMI (Brand Indicators for Message Identification) is a standard that lets verified senders display a brand logo next to authenticated messages in supported inbox clients.
Email Warmup
Domain Warmup, Inbox Warmup
Email warmup is the practice of gradually increasing send volume from a new domain or mailbox while generating positive engagement (opens, replies, removing-from-spam) to build sender reputation with major mail providers.
Soft Bounce
A soft bounce is a temporary delivery failure where the receiving mail server rejects the message with a 4xx SMTP code.
Hard Bounce
A hard bounce is a permanent delivery failure: the receiving server rejects the message with a 5xx SMTP code and the sending platform should not retry.
Reply Rate
Reply rate is the share of recipients who send any reply to a campaign or thread, expressed as a percentage of delivered messages.
Reply Sentiment Analysis
Reply sentiment analysis is an AI classifier applied to inbound email replies that labels each reply as positive, negative, or neutral.
Hot Lead Detection
Hot lead detection is a multi-signal scoring model that ranks prospects by likelihood of converting in the near term (typically 7 days).
Send Time Optimization
Send time optimization (STO) is an AI feature that predicts the hour of day a specific recipient is most likely to engage with email based on their historical open and reply pattern, then schedules outbound messages accordingly.
Email Engagement Score
An email engagement score is a single 0-100 number per prospect combining confidence-scored open count, click count, reply count, reply sentiment, and recency decay.
Office.js Add-in
Office Web Add-in, Outlook Web Add-in
An Office.
Click-Through Rate
CTR
Click-through rate is the share of recipients who click any tracked link in an email, expressed as a percentage of delivered messages.
Unsubscribe Rate
Unsubscribe rate is the share of delivered messages that triggered an unsubscribe action, expressed as a percentage.
Smart Compose
Smart Compose is an AI feature that suggests phrasing, completes sentences, or generates entire email drafts based on the recipient, prior thread context, and sender style.
Inbox Placement
Inbox Placement Rate, IPR
Inbox placement is the share of sent messages that land specifically in the recipient's primary inbox, as opposed to spam, promotions tab, social tab, or quarantine.
Spam Trap
Spamtrap, Honey Pot, Spam Honeypot
A spam trap is an email address operated by an anti-spam organisation, mailbox provider, or blocklist maintainer that is monitored to identify senders with poor list-hygiene practices.
Email Blacklist
Email Blocklist, DNSBL, RBL
An email blacklist (now more commonly called a blocklist) is a DNS-published database of IPs and domains identified as spam sources.
Catch-All Email
Catch-All Address, Catchall Domain
A catch-all email domain is configured to accept mail for any address at the domain, regardless of whether the local part (the part before the @) corresponds to a real mailbox.
MX Record
Mail Exchange Record
An MX (Mail Exchange) record is a DNS entry that designates which mail servers handle inbound email for a domain.
Tracking Link Wrapper
Link Wrapping, Click Tracking URL, Wrapped Link
A tracking link wrapper is a URL that the tracking tool substitutes for the original link in an outbound email.
Email Suppression List
Suppression List, Do Not Email List
An email suppression list is the canonical record of addresses that must not receive outbound mail from the sender.
Mailbox Provider
MBP, Email Service Provider (receiving side)
A mailbox provider (MBP) is the company that hosts inbound email for a domain or consumer, providing storage, spam filtering, and reading interfaces.
Email Throttling
Rate Limiting, Send Rate Throttling
Email throttling is rate-limiting outbound mail to stay within the acceptance thresholds set by receiving mailbox providers.
Double Opt-In
Confirmed Opt-In, COI
Double opt-in is a subscription pattern where the user enters their email address (first opt-in), then receives a verification email and must click a confirmation link (second opt-in) before being added to the active list.
Email Header Analysis
Email Headers, Message Headers, Raw Headers
Email headers are metadata fields at the top of every email message that record the routing path, authentication results, sender identity, and content type.
Transactional Email
Transactional email is a message sent in direct response to a user-initiated action: account verification, password reset, order confirmation, receipt, shipping update.
Cold vs Warm Outreach
Cold outreach is outbound to recipients with no prior relationship: no introduction, no prior conversation, no shared connection.
Email Tracking Pixel Detection
Email tracking pixel detection is the technique of identifying tracking pixels in incoming mail, either to alert the recipient or block the pixel from firing.
Preview Text
Preheader, Preview Snippet
Preview text (also called the preheader) is the short snippet of text visible next to or below the subject line in the inbox list.
Open Tracking vs Click Tracking
Open tracking and click tracking are the two core email tracking mechanisms.
Email Segmentation
Email segmentation is the practice of dividing a list into smaller audience groups based on shared attributes (industry, role, geo), behaviour (opens, clicks, prior purchase), or lifecycle stage (new subscriber, engaged, dormant).
Email Automation
Automated Email, Drip Campaign, Triggered Email
Email automation is the practice of sending email programmatically based on triggers, schedules, or recipient behaviour rather than manually.
Spam Folder vs Quarantine
Spam folder placement and quarantine placement are two different fates for suspect mail.
Engagement Time of Day
Engagement time of day is the distribution of when recipients actually open and engage with received email, plotted by hour of day.