Email Verification & Deliverability Glossary

A

Accept-All Email (Catch-All Email)

An accept-all or catch-all email address belongs to a domain configured to accept every incoming email, regardless of whether the specific mailbox exists.

API (Application Programming Interface)

A programmatic interface that allows developers to integrate email verification directly into their own software, forms, or workflows without manual uploads.

A Record (Address Record)

A DNS entry that maps a domain name to an IPv4 address, telling the internet where to find a server.

Authentication (Email Authentication)

A set of technical standards that verify a sender's identity and protect recipients from spoofed or forged emails.

B

Blacklist (Email Blacklist / DNS Blacklist / DNSBL)

A real-time database maintained by third-party organizations that lists IP addresses or domains known to send spam, phishing, or malicious content.

Bounce (Email Bounce)

Occurs when an email cannot be delivered to the recipient's inbox and is returned to the sender.

Hard Bounce

A permanent, unrecoverable delivery failure where the email server has definitively rejected the message.

Soft Bounce

A temporary delivery failure where the email address is valid and the server is reachable, but delivery failed for a transient reason.

Bounce Rate

The percentage of sent emails that were not delivered.

Bulk Email Verification

The process of uploading and validating an entire email list at once.

C

CAN-SPAM Act

A US federal law enacted in 2003 that sets rules for commercial email and gives recipients the right to stop receiving them.

CASL (Canada's Anti-Spam Legislation)

Canada's anti-spam law governing the sending of commercial electronic messages to Canadian recipients.

Catch-All Email

A catch-all or accept-all email address belongs to a domain configured to accept every incoming email, regardless of whether the specific mailbox exists.

CNAME Record (Canonical Name Record)

A DNS record type that maps one domain name (alias) to another (the canonical domain name).

Complaint Rate (Spam Complaint Rate)

The percentage of email recipients who click 'Mark as Spam' or 'Report Junk'.

D

Data Decay (Email List Decay)

The natural process by which email lists become less accurate over time as people change jobs or abandon addresses.

Deliverability (Email Deliverability)

The ability to successfully land email messages in the recipient's inbox rather than the spam folder or being blocked.

Disposable Email Address (DEA / Temporary Email)

A temporary, throwaway email address created to sign up for services without revealing a real email.

DKIM (DomainKeys Identified Mail)

An email authentication method that uses cryptographic signatures to verify the sender domain and message integrity.

DMARC (Domain-based Message Authentication, Reporting and Conformance)

An authentication, policy, and reporting protocol built on top of SPF and DKIM.

DNS (Domain Name System)

The internet's 'phone book' that translates human-readable domain names into machine-readable IP addresses.

DNS Lookup

The process of querying the DNS system to retrieve records associated with a domain.

Domain Reputation

A trust score assigned to a sending domain by ISPs and email security companies.

Double Opt-In

A subscription process where a user must confirm their email address by clicking a link in a confirmation email.

E

Email Address Structure

The standardized format of an email address: [email protected].

Email Authentication

A set of technical standards that verify a sender's identity and protect recipients from spoofed or forged emails.

Email Hygiene (List Hygiene)

The ongoing practice of cleaning and maintaining your email list to ensure it contains only accurate, active addresses.

Email Validation vs. Email Verification

Validation checks if an address is formatted correctly; Verification confirms if the mailbox actually exists.

Email Verification (SMTP Verification)

A comprehensive process to confirm an email address is valid and deliverable.

ESP (Email Service Provider)

A company that provides email sending infrastructure and campaign management tools.

Engagement (Email Engagement)

How actively recipients interact with your emails through opens, clicks, and replies.

F

False Negative (Verification)

When a valid, deliverable email address is incorrectly flagged as invalid during verification.

False Positive (Verification)

When an invalid or undeliverable email address is incorrectly marked as valid.

Free Email Provider

Webmail providers that offer email addresses to individuals at no cost.

G

GDPR (General Data Protection Regulation)

The EU's data privacy and security law, which treats email addresses as personal data.

Greylisting

A spam filtering technique where a server temporarily rejects emails from unknown senders.

H

Header (Email Header)

Metadata lines prepended to every email containing routing, origin, and authentication info.

Honeypot (Spam Trap Type)

An email address specifically created to catch spammers, never used by a real person.

I

IMAP (Internet Message Access Protocol)

An email retrieval protocol that syncs messages across multiple devices while keeping them on the server.

Inbox Placement Rate

The percentage of sent emails that land in the primary inbox rather than the spam folder.

Invalid Email Address

An email address that cannot receive mail due to syntax errors, non-existent domains, or missing mailboxes.

IP Address (Sending IP)

The numeric identifier of the mail server that sends your outgoing emails.

IP Reputation

A trust score assigned to a specific IP address based on its sending history.

L

List Segmentation

Dividing an email list into smaller groups based on shared characteristics.

Local Part (Email Address)

The portion of an email address before the @ symbol.

M

Mailbox (Email Mailbox)

The storage location on a mail server where incoming emails are held for a specific address.

Mail Server (Mail Exchange Server)

A computer system that sends, receives, routes, and stores email using protocols like SMTP, IMAP, and POP3.

MX Record (Mail Exchange Record)

A DNS record specifying which mail servers are responsible for accepting incoming email for a domain.

N

Non-Existent Domain

A domain that is not registered, has expired, or has no DNS records.

T

TXT Record

A DNS record type used to store text-based information, standard for email authentication.

Transactional Email

Automated emails triggered by user actions (receipts, password resets).

U

Unknown Email (Unverifiable Email)

Indicates the verifier could not definitively determine if an address is valid.

Unsubscribe Link (Opt-Out Link)

A link allowing recipients to easily opt out of future emails.

V

Valid Email Address

An address confirmed to have correct syntax, a valid domain, and an existing mailbox.

W

Warm-Up (IP / Domain Warm-Up)

Gradually increasing email volume from a new IP/domain to build trust with ISPs.

Whitelist

A list of approved senders trusted to bypass spam filters.

Z

Zero Bounce / Hard Bounce Policy

A strict standard where any hard bounce is immediately and permanently suppressed.