A/B testing
A/B testing sends two or more variants of a message to random samples and measures which performs better on a chosen metric before sending the winner to the rest.
Full guide →MailMaid Academy™ / GlossaryPlain words for
Plain words for
technical signals.
90 terms for understanding checks, bounce reports and authentication. Definitions describe the concept, not a guarantee about your messages.
Abandoned cart and browse recovery
Abandoned cart automation sends a timed series to shoppers who added items but did not check out, usually one to three messages over 24 to 72 hours, often with the cart contents embedded.
Full guide →Address syntax
The structural form of an email address. Passing a syntax check does not establish mailbox existence.
Agentic email and MCP
Agentic email uses AI agents with scoped tool access (via protocols like MCP) to read, triage, draft, and send mail under defined policies rather than one-off prompts.
Full guide →AI agents in marketing automation
AI agents extend rule-based automation with judgment: choosing the next message, writing variants, scoring replies, and deciding when to hand off to a human.
Full guide →AI personalization
AI personalization uses language models to generate message content tailored to each recipient from structured data (role, company, recent activity) instead of merge tags alone.
Full guide →AI reply handling
AI reply handling classifies inbound responses (interested, not now, wrong person, unsubscribe, out of office) and drafts or routes the next action automatically.
Full guide →Alignment
A relationship between authenticated domains and the visible From domain under the applicable DMARC mode.
Apple Mail Privacy Protection
Mail Privacy Protection (MPP) is an Apple Mail feature that preloads message content, including tracking pixels, through Apple proxies, hiding the recipient's IP and making opens appear whether or not the person read the message.
Full guide →ARC
A mechanism that records authentication assessments across an intermediary chain. Receiver trust still matters.
Attachment and link security
Attachment and link security covers scanning files and URLs in inbound mail (sandboxing, detonation, URL rewriting and time-of-click checks) and safe handling policies for outbound content.
Full guide →Automated triage
Automated triage uses rules and AI classification to sort incoming mail by urgency and required action before a person sees it.
Full guide →BIMI
A framework for sender logos in participating inboxes, subject to their eligibility requirements.
Blocklists and delisting
Blocklists (Spamhaus, SpamCop, Barracuda, and others) publish IPs and domains observed sending spam. Receivers query them at connection time to reject or filter mail.
Full guide →Bounce handling
Bounce handling is the automated processing of delivery failure notices (DSNs) to classify hard versus soft bounces and suppress addresses accordingly.
Full guide →Business email compromise
BEC is a targeted attack where an attacker impersonates an executive or vendor to redirect payments or extract data, often from a legitimate compromised mailbox rather than a spoofed one.
Full guide →Catch-all
A domain behavior that accepts recipient names without confirming each individual mailbox. Keep its results separate.
Cold email infrastructure
Cold email infrastructure is the set of secondary domains, mailboxes, authentication records, and sending tools used to run outbound campaigns without risking a company's primary domain.
Full guide →Common Mark Certificates
A CMC is a lower-tier BIMI certificate introduced in 2024 for brands without a registered trademark. Eligibility requires 12 months of prior logo use or a government-issued mark. Gmail displays the logo but not the blue checkmark.
Full guide →Complaint feedback loops
Feedback loops (FBLs) are programs run by mailbox providers (Microsoft JMRP, Yahoo CFL, Comcast, and others) that send you a copy or notice whenever a recipient marks your message as spam.
Full guide →Consent and opt-in
Consent is the documented permission a recipient gives to receive marketing email. Laws differ on whether it must be express (opt-in) or may be implied (existing relationship), and on how long it lasts.
Full guide →Content filters
Content filtering evaluates message text, HTML, links, and attachments for spam patterns: deceptive phrasing, URL shorteners, image-only bodies, mismatched link text, and known malicious domains.
Full guide →CRM and email sync
CRM sync keeps contact records, engagement history, and lifecycle stages consistent between a CRM and email tools so sales and marketing act on the same truth.
Full guide →Data retention and DSARs
Data retention policy defines how long mailbox data and marketing records are kept and when they are deleted. DSARs (data subject access requests) require producing or erasing a person's data on request.
Full guide →Dedicated vs shared IPs
A dedicated IP is used only by your mail; a shared IP pool is used by many senders on the same platform. Dedicated IPs give control over reputation but require volume and warm-up; shared pools borrow the platform's reputation.
Full guide →Deduplication
Identifying repeated records under an explicit matching rule while preserving the original data.
Disposable address
An address associated with a short-lived or temporary mailbox service. Local detection covers only known domains.
DKIM
A domain-associated digital signature on message content and selected headers.
DKIM selector
A label used to find the public key associated with a DKIM signature.
DMARC
A domain policy and reporting mechanism built around aligned SPF or DKIM authentication.
DMARC report analysis
DMARC aggregate (RUA) reports are daily XML files sent by mailbox providers listing, per sending IP, how many messages claimed your domain and whether they passed SPF, DKIM, and alignment. Forensic (RUF) reports contain samples of individual failures.
Full guide →DNSBL
A DNS-accessible listing service. Each operator defines its purpose, access terms and removal process.
Domain and IP warm-up
Warm-up is the practice of gradually increasing sending volume from a new domain or IP so mailbox providers can build a positive reputation profile before you reach full volume.
Full guide →Double opt-in
A subscription flow that asks the recipient to confirm the address and intent before activation.
DSN
A delivery-status notification reporting delivery or failure information about a message.
Email design and accessibility
Accessible email design ensures messages render and can be read across clients and by people using screen readers or high contrast: semantic HTML, alt text, sufficient contrast, readable font sizes, and a logical reading order.
Full guide →Email encryption
Email encryption protects messages in transit (TLS between servers, enforced by MTA-STS or DANE) and at rest or end to end (S/MIME, PGP, or portal-based encryption).
Full guide →Engagement metrics
Engagement metrics measure how recipients interact with mail: opens, clicks, replies, forwards, unsubscribes, and complaints. Providers use similar signals to judge sender quality.
Full guide →Enhanced status code
A dotted status code that adds detail to an SMTP outcome, such as 5.1.1.
Follow-up tracking
Follow-up tracking keeps a record of sent messages awaiting a reply and surfaces them when the expected response window passes.
Full guide →Free provider
A service offering personal email addresses. This classification alone is not a reason to block a contact.
Gmail and Yahoo bulk sender requirements
Since February 2024, Gmail and Yahoo require senders of 5,000+ daily messages to authenticate with SPF, DKIM, and DMARC, support one-click unsubscribe, and keep spam complaint rates under 0.3%.
Full guide →Google Postmaster Tools
Google Postmaster Tools is a free dashboard showing how Gmail sees your domain: spam rate, domain and IP reputation, authentication pass rates, encryption, and delivery errors, for senders with meaningful volume.
Full guide →Greylisting
A receiver temporarily defers an unfamiliar delivery attempt. Retry behavior belongs in a controlled queue.
Hard bounce
An operational label for a permanent delivery failure. Review the response to understand the cause.
HIPAA-compliant email
HIPAA-compliant email protects electronic protected health information (ePHI) in transit and at rest, with access controls, audit logs, and a Business Associate Agreement (BAA) with any vendor that handles the mail.
Full guide →Inbox placement
The observed folder location of a received message. Acceptance by a server does not establish this.
Inbox placement testing
Inbox placement is the percentage of sent mail that lands in the primary inbox rather than spam, promotions, or being blocked. It is measured with seed lists across major providers and panel data from real mailboxes.
Full guide →Inbox zero
Inbox zero is a workflow where the inbox is treated as a processing queue rather than storage: every message is archived, delegated, deferred, or acted on, leaving the inbox empty.
Full guide →Labels, filters, and rules
Labels (or folders) and filter rules automatically categorize and route incoming mail based on sender, subject, or content, reducing what reaches the primary view.
Full guide →Lead enrichment and verification
Lead verification confirms that a prospect's address exists and accepts mail before it enters a sequence, using syntax checks, MX lookups, SMTP probing, and catch-all detection. Enrichment adds firmographic and role data used for personalization.
Full guide →Lead scoring
Lead scoring assigns points to contacts based on fit (role, company size) and behavior (clicks, page views, replies) so automations and sales can prioritize and adapt messaging.
Full guide →Lifecycle automation
Lifecycle automation sends messages triggered by where a contact is in their relationship with you: welcome, onboarding, activation, retention, and win-back.
Full guide →List decay
The gradual loss of usefulness or reachability in a contact list. The rate depends on the audience.
List hygiene
List hygiene is the ongoing removal of invalid, inactive, and risky addresses from a mailing list, plus verification of new addresses at the point of capture.
Full guide →Lookalike domain spoofing
Lookalike (cousin) domain spoofing uses a domain visually similar to yours (examp1e.com, example-billing.com) to send mail that passes authentication for the attacker's domain while impersonating your brand.
Full guide →Mailbox account takeover
Account takeover (ATO) is unauthorized access to a legitimate mailbox, typically via phished credentials, password reuse, or OAuth consent phishing.
Full guide →Meeting scheduling from email
Calendar-aware scheduling reads availability and proposes or books times directly from an email thread, removing the back-and-forth.
Full guide →Message variation and spintax
Message variation introduces controlled differences (sentence order, synonyms, structure) across a sequence's sends so that thousands of near-identical messages do not pattern-match as bulk spam.
Full guide →MTA-STS
A domain-published policy intended to strengthen TLS-protected mail transport.
MTA-STS and TLS-RPT
MTA-STS (Mail Transfer Agent Strict Transport Security) lets a domain declare that inbound mail must be delivered over TLS with a valid certificate. TLS-RPT provides reports on delivery failures caused by TLS problems.
Full guide →Multi-step sequences
A sequence is a scheduled series of messages sent to a contact until they reply, click, or complete a goal. Steps are typically spaced days apart and stop automatically on reply.
Full guide →MX record
A DNS record naming a domain’s mail exchanger. SMTP may use address-record fallback when MX is absent.
Onboarding sequences
An onboarding sequence guides new users or customers from signup to first value through timed and behavior-triggered messages that teach, nudge, and celebrate progress.
Full guide →Phishing defense
Phishing is the use of deceptive email to steal credentials, money, or data. Defense combines domain authentication, inbound filtering, user training, and rapid reporting.
Full guide →Re-engagement and sunset policies
A re-engagement campaign targets inactive subscribers with a deliberate attempt to win them back; a sunset policy defines when to stop sending to those who do not respond.
Full guide →Reverse DNS and PTR records
A PTR record maps a sending IP address back to a hostname. Mailbox providers check that the PTR resolves and that the hostname's A record points back to the same IP (forward-confirmed reverse DNS).
Full guide →Role address
A shared function address such as billing or support. It can be legitimate and useful.
Segmentation
Segmentation divides a list into groups based on behavior, lifecycle stage, demographics, or purchase history so each group receives relevant content.
Full guide →Send time optimization
Send time optimization chooses when to deliver each message, either by segment (time zone, historical engagement windows) or per recipient using predicted open behavior.
Full guide →Sender reputation
Sender reputation is the score mailbox providers assign to a sending domain and IP based on complaint rates, bounce rates, engagement, spam-trap hits, and authentication history. It determines whether mail is delivered, filtered, or rejected.
Full guide →Shared inboxes
A shared inbox (support@, sales@) is a mailbox multiple people work from, with assignment, status, and collision detection so no message is answered twice or not at all.
Full guide →SMTP 421
A service-unavailable response associated with closing the connection. Inspect the full server text.
SMTP 451
A temporary processing failure. It does not automatically mean the address is wrong.
SMTP 452
A temporary resource problem. Diagnose the full response and context.
SMTP 550
A permanent rejection often associated with mailbox or policy issues. The reply text matters.
SMTP 552
A storage-allocation rejection. Do not infer a precise cause without the full response.
SMTP 554
A transaction or service rejection. Read the detailed response before acting.
Soft bounce
An operational label for a temporary failure; use a bounded retry policy.
SPF
A policy for authorizing sending hosts for an evaluated mail domain. It is separate from a DKIM signature.
Subdomain delegation for vendors
Subdomain delegation gives each third-party sender its own subdomain (for example news.example.com for the ESP, help.example.com for the helpdesk) with dedicated SPF, DKIM, and DMARC records, so each vendor's reputation and configuration are isolated.
Full guide →Subject lines and preheaders
The subject line and preheader are the two text fields shown in the inbox list before a message is opened. They determine whether a recipient opens, ignores, or reports the message.
Full guide →Suppression
A rule that excludes an address from a send, such as an unsubscribe, complaint or permanent failure.
SVG Tiny PS logos
SVG Tiny 1.2 Portable/Secure is the restricted SVG profile required by BIMI. It forbids scripts, external references, and embedded raster images, and requires a <title> element and baseProfile="tiny-ps".
Full guide →TLS-RPT
Reporting of mail transport security outcomes to a domain’s designated reporting destination.
Transactional vs marketing email
Transactional email is triggered by a user action (receipts, password resets, alerts) and is exempt from most marketing consent rules. Marketing email promotes products and requires consent and unsubscribe links.
Full guide →Triggers and webhooks
Triggers are events (form submission, purchase, page view, CRM stage change) that start or advance an automation. Webhooks and APIs carry those events between systems.
Full guide →Unknown verdict
The available evidence could not resolve the check. It is neither a successful verification nor a permanent failure.
Unsubscribe requirements
Unsubscribe compliance covers the legal and provider requirements for letting recipients opt out: a visible link, one-click List-Unsubscribe headers (RFC 8058), and processing within a defined window.
Full guide →Verified Mark Certificates
A VMC is an X.509 certificate issued by an approved authority (DigiCert or Entrust) that binds a registered trademark logo to a domain. Gmail and Apple Mail require a VMC or CMC to render a BIMI logo.
Full guide →