Email proofing glossary

The vocabulary of email review, previewing, and sending domains, in plain language. These are the terms that come up when a campaign moves from a finished design to a confident send — and most of them link to a free tool that shows you the thing itself.

Email proofing: Reviewing a finished email campaign for mistakes — copy, design, links, and rendering — and collecting feedback before it is sent. Proofing is the quality check between "design done" and "cleared to send."; See how proofing works in Proofel
Email preview: Rendering an email exactly as subscribers will see it — across desktop and mobile widths, different mail clients, and dark mode — before it is sent. Clients differ enough (Outlook renders with the Word engine; Gmail clips at 102KB) that a preview catches problems an ESP editor hides.; Try the free email preview tool
Email approval workflow: The process of routing an email campaign to the people who must sign off — a manager, a client, legal — and recording their decision. A clear workflow replaces reply-all threads with a single, auditable Approve or Request changes.; Approvals and guest reviewers
Pixel-pinned annotation: A comment attached to an exact point on the rendered email, shown as a numbered marker. Instead of describing "the button under the hero," a reviewer pins the note directly on the button so there is no ambiguity.; Review and annotate
Guest reviewer: Someone who reviews or approves an email without a Proofel account. They open a share link, enter a display name, and can comment, annotate, and approve in the browser — including on a phone.; How guest review works
Share link vs approval link: A share link collects feedback; an approval link asks for a decision. Opening an approval link lets the reviewer Approve or Request changes, and the decision is recorded in the audit trail.; Sharing and approvals guide
Version and version compare: Each new draft of an email is captured as a numbered version. Comparing two versions side by side — or with a draggable wipe divider — shows exactly what changed between drafts, with each comment kept on the version it was made on.; Versions and compare guide
Multiple approvers: An approval that requires more than one sign-off before a campaign is marked Approved. Every reviewer you add gets the same link at once, in no set order — useful for regulated or high-stakes sends where several stakeholders must agree.; Multi-approver routing
Client simulation (deterministic simulation): Predicting how a mail client will render an email by transforming the HTML the way that client does — stripping the CSS it drops, rewriting what it rewrites — and rendering the result, rather than photographing a real device. Because the colour model and the CSS survive the transform, a finding can name the exact declaration that broke. The tradeoff is that it cannot reproduce a pixel-exact classic-Outlook layout.; How our simulation works, and where it can be wrong
Client lens: A single client, browser, and operating-system combination applied to a preview — Gmail on Chrome, Outlook on Windows, Apple Mail on iOS — mapped to the engine that actually renders it (Blink, WebKit, Gecko, or Word) so only that engine's documented limitations are applied.; Preview through 20 client lenses
Outlook Word engine: Outlook 2007 to 2024 for Windows lays email out with Microsoft Word's HTML engine rather than a browser engine. It has no support for border-radius, box-shadow, flexbox, or grid, applies its own table model, and scales at 120 DPI unless told otherwise — which is why the same email can look modern everywhere else and plain there.; Lint your HTML against Word-engine constraints
Client support matrix: A per-declaration verdict on which mail clients support what your email actually uses, drawn from the Can I email? dataset (caniemail.com, MIT licensed). Rather than looking a feature up, the matrix walks your CSS and flags the usages a modelled client will drop, with the source line. It reflects the newest tested version of each client, so "no findings" means nothing recognised is risky, not that the email is safe everywhere.; Run the support matrix on your email
Dark-mode simulation: A preview of how an email looks when a mail client applies dark mode. Clients differ: Apple Mail honors authored dark CSS with a partial inversion, while Gmail and Outlook force a full color inversion. Proofel models each separately by converting colours to CIELAB, inverting lightness, and converting back, which preserves hue while flipping luminance. Images are never inverted, exactly as no real client inverts them.; Simulate dark mode in the free preview tool
Blocked images: Many mail clients and corporate gateways do not load remote images until the reader asks them to. An email whose message lives inside a hero image therefore arrives as empty boxes and alt text, so previewing with images off shows what a first-open reader actually sees.; Preview with images blocked
Gmail clipping (102KB): Gmail hides part of any message whose HTML is larger than roughly 102KB behind a "Message clipped" link, which can bury content and even the unsubscribe link. Keeping the HTML under that threshold prevents clipping.; Shrink an email with Email Cleanup · Locate the clip line in the free preview tool
Preheader: The snippet of text a mail client shows next to or beneath the subject line in the inbox list. Clients take it from the first readable text in the email, so a hidden preheader block near the top of the HTML is how you control it deliberately instead of letting "View in browser" become your pitch.; See your preheader in ten real inbox rows
Preheader spill: When an authored preheader is shorter than the space a client gives the snippet, the client keeps reading into the body and appends whatever comes next — a navigation label, a legal line, "View in browser". The fix is padding the hidden preheader with zero-width characters so nothing spills in behind it.; Check for spill in the subject line tool
Inbox truncation: The point at which a mail client stops showing your sender name, subject, or preheader in the inbox list. It is decided in pixels, not characters: each client uses its own font stack, size, weight, and column width, so the same subject cuts at different words in Gmail, Apple Mail, and Outlook. A character count cannot answer the question.; Measure truncation across ten inbox rows
Merge tag: A placeholder in an email that an ESP replaces with subscriber data at send time — {{first_name}}, *|FNAME|*, %%city%%. Each ESP has its own syntax, and an unrendered tag reaching the inbox is one of the most visible mistakes an email can make, especially in a subject line.; Catch unrendered merge tags before you send
WCAG AA contrast: The Web Content Accessibility Guidelines 2.1 level AA threshold for text legibility: a contrast ratio of at least 4.5:1 against its background, or 3:1 for large text (18.66px, or 14px bold and above). Email is held to the same bar as the web, and small grey captions on white are the usual failure.; Measure contrast in your email
Contrast in a dark inversion: A colour pair that passes WCAG AA as authored can fail once Gmail or Outlook force-inverts it, because the two colours do not move by the same amount. Measuring contrast a second time inside the inverted render is the only way to catch it — and it is a finding a screenshot-based tool structurally cannot produce, because a photograph has no colour model left to measure.; Measure contrast inside a Gmail dark inversion
Colour-vision-deficiency lens (CVD): A transform that shows an email as a reader with protanopia, deuteranopia, or tritanopia perceives it, using the Machado, Oliveira and Fernandes (2009) matrices applied in linear light. It is how you find out that your "red means error, green means success" badge pair is one colour to roughly one man in twelve.; Apply colour-vision lenses to your email
Screen-reader read order: The sequence in which assistive technology announces an email: heading levels, link text, image alt text, and table content, in document order rather than visual order. Layout tables without role="presentation" get announced as data tables, and a link that reads only "click here" tells a listener nothing.; Read the announcement transcript for your email
Pre-send report: A scored run of static checks over a finished email — clipping risk, a missing unsubscribe link, placeholder links, image alt text, dark-mode readiness, contrast, client support, and Outlook constraints — presented worst-first with a 0 to 100 score. The deductions are chosen severity weights, not an industry standard; the score is a triage order, not a guarantee.; Score your email in the all-in-one checker · Run a pre-send report on your email
All-in-one email check: Running every pre-send engine over one pasted email in a single pass, and presenting the result summary-first: a score, then the two or three findings worth fixing first, then the repairs a machine can make, then the full per-engine detail. The alternative — picking the right single-purpose checker yourself — asks you to already know whether the problem is contrast, Outlook, or clipping, which is the one thing you do not know before you check.; Run the free all-in-one email checker
Auto-fix (one-click fix): A mechanical, deterministic repair applied to email HTML — adding role="presentation" to layout tables, lang and a viewport meta, mso-line-height-rule, the MSO PixelsPerInch block, rel="noopener", max-width and dimensions on images, alt="" on decorative images, zeroed cellpadding, and an empty preheader block: eleven in total. Every fix is idempotent, changes attributes rather than the visible design, and never invents content, so no alt text, preheader copy, or link destination is written for you. Reading the list of fixes an email needs is free with no account; applying them, which produces the rewritten HTML, is part of a paid plan.; See which findings are auto-fixable
Mechanical fix vs judgement call: The line an automatic fixer should refuse to cross. A mechanical fix has exactly one correct answer a machine can compute: a layout table needs role="presentation", a target="_blank" link needs rel="noopener". A judgement call depends on meaning or taste, so it needs a person: what the alt text should say, which colour to change to clear a contrast failure, what the subject line should be. A tool that blurs the two will quietly report a judgement call as fixed, which is worse than leaving it on the list.; What the checker fixes, and what it hands back to you
Fix list vs fixed output: The two halves of any automatic-repair offer. The fix list is the diagnosis: which repairs apply to this email and how many places each one touches. The fixed output is the rewritten HTML itself. They are worth separating because they have very different value — the diagnosis is most of the usefulness and costs nothing to give away, which is why Proofel shows the complete list to everyone and charges only for applying it.; See the fix list on your own email
Image weight: The real byte size of each image an email loads, plus its intrinsic dimensions and whether it animates. It is what decides whether the email feels instant on a phone on mobile data, and it is invisible in an ESP editor. Measuring it needs the bytes themselves, so a cross-origin image has to be fetched through a proxy before its weight can be read at all.; Audit every image in your email
Placeholder link: An href left at a stand-in value — #, about:blank, http://example.com, or an unreplaced merge tag — in a finished email. It is the single most expensive proofing miss, because the campaign sends, the CTA is clicked, and nothing happens.; Find placeholder links in your HTML · Screenshot every link destination
SpamAssassin score: The rule-based score Apache SpamAssassin, a widely deployed open-source filter, assigns a message. It is one filter, not Gmail, Outlook.com, or Yahoo, all of which use proprietary systems fed by sender reputation and recipient behaviour, and a check run without a real send fires preview-only rules (NO_RECEIVED, NO_RELAYS, MISSING_DATE) that are artefacts of testing rather than delivery problems.; Get a SpamAssassin score for your email
Link visualizer: A tool that extracts every hyperlink in an email, follows redirects to the final destination, and captures a live screenshot plus HTTP status for each — so wrong URLs, dead pages, and stale tracking links are caught before sending.; How the Link Visualizer works
SPF: Sender Policy Framework: a DNS TXT record listing which servers are allowed to send mail for your domain. A receiving server checks the sending IP against it. Only one SPF record may exist per domain, resolving it must not take more than ten DNS lookups (RFC 7208), and ending it in +all defeats the point entirely.; Check your domain's SPF record
DKIM: DomainKeys Identified Mail: your sending platform signs each message with a private key, and the matching public key is published in DNS under a named selector. A receiver verifies the signature, which proves the message was authorised by your domain and has not been altered in transit.; Probe your DKIM selectors
DMARC: A DNS policy that tells receivers what to do when a message claiming your domain fails SPF and DKIM alignment: none (monitor only), quarantine, or reject. It also asks for aggregate reports so you can see who is sending as you. Gmail and Yahoo now require it for bulk senders, and p=none is a starting point rather than a destination.; Read your DMARC policy and alignment
BIMI, MTA-STS and TLS-RPT: Three optional records that sit on top of authentication. BIMI publishes a verified logo some clients show beside your messages, and requires DMARC at enforcement. MTA-STS tells sending servers to require TLS when delivering to you, closing a downgrade attack. TLS-RPT asks for reports when that fails. None of them affect whether an email renders; they affect whether it is trusted.; Check BIMI, MTA-STS and TLS-RPT
.eml file: A standard file format (RFC 5322 MIME) that stores a single email — its subject, sender, headers, and HTML, with any inline images attached. Exporting an email as .eml lets you open it in a mail client or hand it off to whoever sends the campaign.; Open a .eml file in your browser
Tracking pixel: A tiny invisible image an email service provider adds to measure opens. When an email is ingested for review, Proofel skips these pixels so proofing does not fire false open events.; How emails get into Proofel

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