Email terminology glossary

An SPF record is a DNS TXT record that lists which servers are allowed to send mail for a domain, checked against the envelope return-path rather than the visible From address.

DKIM signs outgoing mail with a private key and publishes the matching public key in DNS, so a receiver can verify the message was not altered in transit and genuinely came from the signing domain.

DMARC is a DNS TXT record that tells receivers what to do with mail claiming your domain that fails SPF and DKIM alignment, and where to send reports about it — the enforcement layer on top of both.

BIMI is a DNS record that points a supporting mailbox provider at a domain's SVG logo, displayed next to authenticated mail — but only once DMARC is already enforcing.

MTA-STS (RFC 8461) lets a domain require that inbound mail delivered to it use encrypted, authenticated SMTP, closing the downgrade and interception attacks plain SMTP TLS leaves open.

TLS-RPT (RFC 8460) is a DNS record naming an address that receives daily aggregate reports of SMTP transport-security failures against your domain, the reporting half of MTA-STS.

The DKIM selector is the label a sender chooses to name a specific public key at <selector>._domainkey.<domain>, letting one domain publish and rotate several DKIM keys at once.

DMARC alignment is the check that ties a passing SPF or DKIM result back to the domain in the visible From header, using either a strict exact-match mode or a relaxed organizational-domain match.

The return-path is the envelope-level sender address SPF actually checks and where non-delivery bounces are sent — distinct from, and invisible next to, the visible From address a recipient reads.

A soft bounce is a temporary delivery failure — a full mailbox, an unreachable server, an oversized message — reported with an SMTP 4xx code, meant to be retried rather than treated as permanent.

A hard bounce is a permanent delivery failure — the address or domain doesn't exist — reported with an SMTP 5xx code, and the address should never be sent to again without a fresh, confirmed reason to believe it's valid.

Complaint rate is the share of delivered messages a recipient actively marked as spam, and AWS reviews an SES account at 0.1% and may pause sending at 0.5% — thresholds far tighter than the bounce-rate ones.

A spam trap is an email address mailbox providers or anti-spam organizations control specifically to catch senders with poor list hygiene — a hit confirms the practice, not a one-off mistake.

A blocklist (DNSBL) is a DNS-queryable list of IPs or domains associated with unwanted mail — checked by reversing the IP into a lookup subdomain and testing for a listing response.

IP warming is the gradual, staged increase of sending volume on a new IP so mailbox providers can build a reputation baseline for it before it carries full-scale traffic.

A dedicated IP is a sending IP address assigned to a single sender rather than shared across many, meaning its reputation is entirely and exclusively yours to build and protect.

A shared IP is a sending address used by many senders at once, whose reputation reflects the collective behavior of everyone in the pool rather than any single sender's own history.

Inbox placement is whether a message that was successfully delivered actually lands in the primary inbox, a secondary tab, or the spam folder — a decision no sender, including AWS, can see or guarantee from the outside.

A feedback loop is a mailbox provider's mechanism for forwarding a recipient's spam complaint back to the sending infrastructure, so the address can be suppressed and the underlying cause investigated.

List-Unsubscribe is an email header that lets a mailbox client render a working unsubscribe action directly in its interface, and it's mandatory for bulk senders on Gmail and Yahoo as of February 2024.

An SMTP relay accepts mail over the standard SMTP protocol and forwards it on, letting any system that only knows how to speak SMTP — not call an API — send through a provider like SES.

An MX record is a DNS record naming which mail server accepts email for a domain, with a priority value that determines the order receiving servers should be tried in.

A configuration set is an SES resource attached to a send that controls where its events publish, which reputation options apply, and which IP pool it uses — a routing and policy layer on top of the send itself.

The suppression list is SES's account-level record of addresses it will refuse to send to, populated automatically on a hard bounce or a complaint, unless a send explicitly overrides it.

SES enforces two independent sending caps — a rolling 24-hour maximum message count and a per-second maximum rate — and hitting either returns a different exception with a different fix.

Message-ID is the RFC 5322 header uniquely identifying an individual email message; SES's own MessageId, returned from a successful send, is the handle used to correlate that send with its later delivery, bounce, and complaint events.

Double opt-in requires a subscriber to confirm their email address — usually by clicking a link in a confirmation message — before they're added to a sending list, rather than trusting the signup form alone.

CAN-SPAM is the 2003 US federal law, enforced by the FTC, that requires accurate sender information, a working opt-out mechanism honored within 10 business days, and a valid physical postal address in commercial email.

GDPR requires a lawful basis for processing personal data, and for marketing email that basis is generally consent — freely given, specific, informed, and an affirmative opt-in, not a pre-checked box or a default-in setting.

Open rate is the share of delivered messages whose tracking pixel fired — historically the headline engagement metric, but heavily inflated since 2021 by Apple's Mail Privacy Protection pre-fetching images regardless of whether a message was actually opened.