---
title: "Email Verification Glossary - Emvero"
description: "Definitions of catch-all domains, MX records, SMTP replies, DNS failures and other email verification terms, with the limits of each check."
url: https://emvero.io/glossary/
language: en
updated: 2026-10-01
---

Email verification glossary

# Email verification terms and what they mean

Look up a term from a verification result or a mail-server response. Each entry explains the mechanism, what the evidence establishes and where uncertainty remains. Start with the term you need below.

## Find a definition

### Catch-all domain

A mail server accepts arbitrary recipients, so acceptance alone cannot establish whether a particular mailbox exists.

### Greylisting

A temporary SMTP refusal asks the sender to try again. A later attempt may provide more evidence.

### Spam trap

An address used to identify problematic sending practices. A verification check cannot certify that an address is not a trap.

### Role account

An address for a team or function, such as support@. It can receive mail; its suitability depends on the purpose.

### Disposable email address

An address at a temporary-mail provider. The domain signal concerns durability and policy, rather than proving delivery failure.

### Hard bounce and soft bounce

Permanent and temporary delivery failures describe a sending attempt. Learn how they differ from verification evidence.

### SMTP handshake

The greeting and commands used to ask a mail server about a recipient, stopping before message content is sent.

### MX record

A DNS record that identifies a domain’s mail servers and their priority. A mail route does not prove that a mailbox exists.

### Email address syntax

Address-format rules checked before network lookups. A valid format does not establish a working domain or mailbox.

### DNS failure

A domain lookup may report nonexistence or a temporary resolution problem. Those outcomes require different handling.

### Throttling and rate limiting

A destination limits how often probes can connect or ask about recipients. The limit does not establish mailbox existence.

### Ambiguous rejection

A recipient refusal can hide mailbox information or reflect server policy. A permanent-looking reply need not justify rejection.

### TLS and STARTTLS failures

An attempted STARTTLS upgrade fails before the recipient check. Missing STARTTLS support and certificate validation are separate questions.

### Policy rejection

A destination refuses a session or recipient under its own rules. The refusal alone cannot establish that the mailbox is absent.

### Codes that describe us, not the address

Service protections, capacity limits or incomplete work can prevent a probe. These codes explain the check, rather than the mailbox.

### Protocol errors

A reply or exchange cannot be processed within the SMTP client’s protocol and resource limits. A valid negative reply is a different case.

### Addresses this service will not probe

An unsupported address form or unsafe destination can stop the check by design. The limitation does not prove delivery failure.

## See the evidence for an address

Create an account to run a check and read its status, recommended action and reason codes.

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