# Email Terminology Glossary Source: https://wraps.dev/glossary 30 terms, grouped by what they're actually for. Every authentication entry is written from what Wraps' deliverability checker evaluates, not from general knowledge — where a failure mode already has its own page, this links to it instead of restating it. Part of the Wraps [Learning Center](https://wraps.dev/learning). ## Authentication The mechanisms a receiver checks to decide whether mail claiming to be from your domain actually is. - [SPF (Sender Policy Framework)](https://wraps.dev/glossary/spf) 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 (DomainKeys Identified Mail)](https://wraps.dev/glossary/dkim) 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 (Domain-based Message Authentication, Reporting & Conformance)](https://wraps.dev/glossary/dmarc) 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 (Brand Indicators for Message Identification)](https://wraps.dev/glossary/bimi) 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 (SMTP MTA Strict Transport Security)](https://wraps.dev/glossary/mta-sts) 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 (SMTP TLS Reporting)](https://wraps.dev/glossary/tls-rpt) 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. - [DKIM selector](https://wraps.dev/glossary/dkim-selector) The DKIM selector is the label a sender chooses to name a specific public key at .\_domainkey., letting one domain publish and rotate several DKIM keys at once. - [DMARC alignment](https://wraps.dev/glossary/dmarc-alignment) 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. - [Return-path](https://wraps.dev/glossary/return-path) 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. ## Deliverability What happens to a message after it authenticates — whether it bounces, gets reported, or actually lands. - [Soft bounce](https://wraps.dev/glossary/soft-bounce) 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. - [Hard bounce](https://wraps.dev/glossary/hard-bounce) 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](https://wraps.dev/glossary/complaint-rate) 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. - [Spam trap](https://wraps.dev/glossary/spam-trap) 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. - [Blocklist (DNSBL)](https://wraps.dev/glossary/blocklist) 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](https://wraps.dev/glossary/ip-warming) 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. - [Dedicated IP](https://wraps.dev/glossary/dedicated-ip) 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. - [Shared IP](https://wraps.dev/glossary/shared-ip) 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](https://wraps.dev/glossary/inbox-placement) 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. - [Feedback loop (FBL)](https://wraps.dev/glossary/feedback-loop) 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](https://wraps.dev/glossary/list-unsubscribe) 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. ## Infrastructure The AWS SES resources and protocols that carry a send from an application to a recipient's mail server. - [SMTP relay](https://wraps.dev/glossary/smtp-relay) 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. - [MX record](https://wraps.dev/glossary/mx-record) 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. - [Configuration set](https://wraps.dev/glossary/configuration-set) 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. - [Suppression list](https://wraps.dev/glossary/suppression-list) 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. - [Sending quota](https://wraps.dev/glossary/sending-quota) 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](https://wraps.dev/glossary/message-id) 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. ## Compliance The consent and disclosure rules that decide whether you were allowed to send the message at all. - [Double opt-in](https://wraps.dev/glossary/double-opt-in) 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 Act](https://wraps.dev/glossary/can-spam) 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 consent](https://wraps.dev/glossary/gdpr-consent) 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. ## Metrics The numbers senders watch, and where they quietly stop meaning what they used to. - [Open rate](https://wraps.dev/glossary/open-rate) 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.