Adapter

An object implementing EditorStorageAdapter, through which the editor reads and writes templates, versions, saved rows and images. Every method is optional. See Storage adapters.

Block

A leaf content node — paragraph, heading, image, button. Registered in the block registry. Sometimes called a component in the document tree; they are the same thing.

Canvas

Two meanings, both ours. (1) The email body’s own settings — width, padding, background, preheader, language — serialised as the canvas key of a template. (2) The editing surface in the editor UI. Neither is an HTML <canvas>.

Capabilities

An object that restricts what the editor’s UI offers. It can only take away, never grant.

Component

A node in the document tree: { id, type, componentType?, props }. Interchangeable with block.

Context

A flat key–value map supplied at render time, evaluated against visibility rules. Context values are never injected into content — they only decide what is shown.

Document

The template JSON — the five-key object the editor exports and the renderer consumes. See Template schema.

Hydrate

Restore stripped default values when a template is loaded. The inverse of optimize.

Merge tag

A group-qualified placeholder such as {{ text.first_name }}, replaced at render time. The prefix decides escaping.

Optimize

Strip every property equal to its default before serialising. The inverse of hydrate. The invariant is hydrate(optimize(x)) ≡ x.

Prune

Evaluate visibility rules now and emit only the matching branches. What render() always does.

Render target

An output format: html, mjml, or react-email.

Row

A horizontal band containing columns. Rows can nest, to a depth of 5.

Row spacer

A row whose only job is vertical space.

Saved row

A reusable row stored in a library. Two libraries exist: the user’s own (writable) and a shared one (read-only).

Schema version

major.minor on a template. Only the major is enforced for compatibility.

Snapshot

{ rows, canvasStyles, name?, tags?, updatedAt? } — what the storage adapter persists. Not identical to a document.

Teleport target

An element inside the editor that all floating UI renders into, keeping it within the shadow root.

Visibility rule

A condition attached to a row or component, evaluated against context.

Wrap

Keep every conditional branch and emit the ESP’s own syntax for it to evaluate at send time. The alternative to prune.

Alignment

In DMARC: the requirement that the SPF- or DKIM-authenticated domain match the domain in the visible From: header. Authentication passing is not the same as aligning, and this is the most commonly missed distinction in email authentication.

ARC

Authenticated Received Chain. Preserves authentication results across forwarding hops, so a forwarded message can still be judged on its original authentication.

BIMI

Brand Indicators for Message Identification. Displays your logo beside the sender name in supporting clients. Requires DMARC at quarantine or reject, and often a paid certificate. Not a deliverability feature.

Bulk sender

Roughly 5,000 or more messages per day to a given provider’s consumer addresses. Bulk senders face additional authentication, unsubscribe and complaint-rate requirements.

Clipping

Gmail truncating a message past roughly 102 KB and showing "View entire message". What gets cut is whatever is at the bottom — usually the unsubscribe link and tracking pixel.

Dark mode strategy

How a client alters colours in dark mode. Four distinct behaviours exist across major clients, ranging from "leave author colours alone" to "swap near-black and near-white" to "no handling at all".

DKIM

DomainKeys Identified Mail. The sending server signs the message with a private key; the public key is published in DNS. Survives forwarding, unlike SPF.

DMARC

A DNS policy stating what to do when SPF and DKIM both fail to align, plus a reporting address. Its reports are often more valuable than its policy.

ESP

Email Service Provider — Klaviyo, Mailchimp, Braze, SendGrid, Resend, Postmark, and so on. Maildeno is not an ESP; it produces the email and hands it to yours.

Envelope sender

The MAIL FROM address in the SMTP conversation. Distinct from the visible From: header, and the distinction is the basis of SPF-versus-DMARC alignment.

MJML

A markup language that compiles to responsive email HTML. One of Maildeno’s three render targets.

MSO conditional

An <!--[if mso]> comment that only Microsoft clients act on. How Outlook fallbacks are delivered — which is why stripping comments from email HTML breaks Outlook.

MTA

Mail Transfer Agent — the server that actually moves mail. Postfix, Exim, and the sending infrastructure behind every ESP.

One-click unsubscribe

The List-Unsubscribe and List-Unsubscribe-Post headers (RFC 8058) that make a provider show a native Unsubscribe control. A footer link alone does not satisfy this.

Preheader

The short line shown after the subject in an inbox list. If unset, clients grab the first line of body copy instead.

PTR record

Reverse DNS for a sending IP. Set at the IP level rather than the domain level, which is why it is easy to forget after a migration.

React Email

A React-based email framework. One of Maildeno’s three render targets — the output is .tsx source, not a rendered component.

Spam rate

The proportion of delivered messages recipients mark as spam. Providers publish thresholds; the practical target is well below the stated ceiling.

SPF

Sender Policy Framework. A DNS record listing which servers may send mail as your domain. Subject to a 10-DNS-lookup limit, and usually broken by forwarding.

VML

Vector Markup Language. Still the only way to render gradients and background images in Outlook desktop.

Warmup

Ramping send volume on a new IP or domain over weeks, starting with the most engaged recipients, so the first signals a provider sees are positive.

Conditional exports

A package.json feature letting one import specifier resolve to different files per runtime. How @maildeno/renderer ships a Node build and an edge build behind one import.

Custom element

A native browser component defined with customElements.define. <maildeno-editor> is one, which is why the editor works in any framework.

Edge runtime

A JavaScript runtime built on V8 isolates rather than containers — Cloudflare Workers, Vercel Edge, Deno Deploy. Fast to start, but with no filesystem and limited Node compatibility.

Light DOM

Ordinary page DOM, as opposed to shadow DOM. The editor’s shadowDom: false mode, offered as an escape hatch when predictable DOM behaviour matters more than style isolation.

Shadow DOM

An encapsulated DOM subtree with its own style scope. The editor’s default. It also retargets event.target, hides content from document.querySelector, and ignores @font-face.

V8 isolate

A lightweight, independent JavaScript execution context. What makes edge runtimes start in single-digit milliseconds where a container cannot.

WebAssembly (Wasm)

A portable binary instruction format. The Maildeno render engine is Rust compiled to Wasm, which is how output stays byte-identical across every runtime.