Email Marketing & Deliverability Glossary

SMTP

Simple Mail Transfer Protocol is the standard protocol used to transfer email between mail systems.

SPF

Sender Policy Framework is a DNS-based mechanism that lists servers authorized to send mail for a domain.

DKIM

DomainKeys Identified Mail adds a cryptographic signature to email so receiving systems can verify that authorized infrastructure signed the message.

DMARC

Domain-based Message Authentication, Reporting and Conformance builds on SPF and DKIM and lets a domain publish an alignment and policy strategy.

MX record

A Mail Exchange record tells sending systems which mail servers accept mail for a domain.

PTR / rDNS

A PTR record maps an IP address back to a hostname and is commonly used as part of mail-server identity checks.

BIMI

Brand Indicators for Message Identification is a standard that can allow a brand logo to be displayed by supporting mailbox providers when requirements are met.

TLS

Transport Layer Security encrypts data in transit between systems that negotiate a secure connection.

Hard bounce

A hard bounce is a permanent delivery failure, such as an invalid or nonexistent recipient address.

Soft bounce

A soft bounce is a temporary or potentially recoverable delivery failure, such as a full mailbox or transient server problem.

IP reputation

A measure influenced by how receiving systems view traffic from a sending IP, including complaint and delivery behavior.

Domain reputation

A reputation signal associated with a sending domain and its historical email behavior.

IP warming

The gradual increase of sending volume from a new IP while monitoring delivery and engagement signals.

Spam complaint

A recipient or mailbox signal indicating that a message was unwanted or reported as spam.

SMTP relay

A mail server or service that accepts a message from one system and relays it toward the recipient system.