Glossary of Email Verification Terms

A quick reference for terms used throughout Mailthentic and the email verification industry.

Bounce (Hard)

A permanent delivery failure. The recipient address doesn't exist or the domain can't receive email. SMTP codes: 550, 553.

Bounce (Soft)

A temporary delivery failure. The recipient's mailbox may be full, the server may be down, or the message was too large. SMTP codes: 450, 451, 452.

Catch-All Domain

A domain configured to accept email for any address, whether or not the specific mailbox exists. Makes individual verification unreliable.

Confidence Score

A percentage (0–100) indicating how certain Mailthentic is about a verification result. Higher scores mean more certainty.

Disposable Email

A temporary email address from services like Mailinator or Guerrilla Mail. Typically used to avoid providing a real address.

DKIM (DomainKeys Identified Mail)

An email authentication method that adds a cryptographic signature to messages, allowing receivers to verify the sender's identity.

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

A policy framework that builds on SPF and DKIM to specify how unauthenticated messages should be handled (none, quarantine, reject).

DNS (Domain Name System)

The internet's directory that translates domain names to IP addresses and stores records like MX, SPF, and DMARC.

Greylisting

An anti-spam technique where a mail server temporarily rejects messages from unknown senders, expecting legitimate senders to retry.

MX Record (Mail Exchange)

A DNS record that specifies which mail server(s) handle email for a domain.

RCPT TO

The SMTP command used to specify the recipient of an email. Mailthentic uses this command to check if a mailbox exists.

Role-Based Email

A generic email address tied to a function rather than a person (e.g., info@, admin@, support@, sales@). Often routes to a shared inbox.

Sender Reputation

A score assigned to your sending IP and domain by mailbox providers, based on bounce rates, spam complaints, and engagement. Higher reputation = better inbox placement.

SMTP (Simple Mail Transfer Protocol)

The standard protocol for sending email between servers. Mailthentic uses SMTP commands (without sending actual messages) to verify mailboxes.

SPF (Sender Policy Framework)

A DNS record that lists which IP addresses are authorized to send email on behalf of a domain.

STARTTLS

An SMTP extension that upgrades a plain-text connection to an encrypted (TLS) connection.