Your Email Sent. That Doesn't Mean It Works.
Every email in your Sandbox inbox is automatically scored across five dimensions — HTML compatibility, broken links, spam signals, performance, and AI content analysis. Not just a number. Specific issues. Exact locations. Actionable fixes
WHY SCORING MATTERS
Your email sent successfully. That doesn't mean it worked.
A successful SMTP response tells you one thing — the server accepted the message. It tells you nothing about whether the email rendered correctly in Outlook, whether the unsubscribe link is broken, whether SpamAssassin would flag the subject line, or whether the CTA is clear enough for anyone to click.
These failures don't show up in logs. They show up in spam complaints and support tickets — after real users have already seen the broken email.
Email Scoring catches all five categories before the email leaves your test environment.
Automatic on arrival. Deeper analysis on demand.
Three scores run automatically
Two scores run on demand
Issues are specific - not just a number
Re-scoring workflow
Send it knowing it's ready — not hoping it is.
Every email in your Sandbox inbox is scored automatically. HTML, links, spam signals — on arrival. Performance and AI analysis — on demand. All five dimensions. One place.
Automatic scoring on every email
Five dimensions — specific issues per score
No separate spam testing tool needed
Free forever on basic plan
Does your email render correctly in the clients your users actually use?
Every CSS property, HTML tag, and layout technique in your email is validated against real email client support data — Gmail, Outlook, Apple Mail, and major mobile clients. Not browser support. Email client support. They are not the same thing.
CSS properties that render fine in Chrome but break in Outlook 2019
HTML attributes not supported in Gmail's rendering engine
Layouts that collapse on mobile clients
Missing or malformed DOCTYPE declarations
Inline vs external CSS conflicts that behave differently per client
What a flagged issue looks like:
Why this matters:
Outlook alone has several rendering engines across its versions — none of which behave like a browser. An email that looks perfect in Gmail can be completely broken in Outlook 2019. HTML Check tells you before a single real user opens it.
What a flagged issue looks like:
Why this matters:
Outlook alone has several rendering engines across its versions — none of which behave like a browser. An email that looks perfect in Gmail can be completely broken in Outlook 2019. HTML Check tells you before a single real user opens it.
What a flagged issue looks like:
Why this matters:
A broken unsubscribe link isn't just a bad experience — it's a compliance issue. A broken CTA in your password reset email means a user who can't get back into their account. Link Check catches both before they affect anyone.
What a flagged issue looks like:
Why this matters:
A broken unsubscribe link isn't just a bad experience — it's a compliance issue. A broken CTA in your password reset email means a user who can't get back into their account. Link Check catches both before they affect anyone.
Every URL in your email. Verified live.
Every URL your email contains — CTAs, unsubscribe links, image source URLs, tracking pixels, footer links — is requested and verified. Live, broken, or redirecting to a dead end.
URLs returning 404
Staging environment URLs left in production templates
Redirect chains that end at an error page
Unsubscribe links that return errors
Image source URLs that are inaccessible
A full health check on your email's production readiness.
Four dimensions evaluated in one score — covering the technical, compliance, accessibility, and content layers of your email.
Technical Foundation
Email file size, image sizes, total estimated load time, HTML complexity, and rendering performance across clients. Heavy emails get clipped by Gmail. Oversized images break on mobile. This dimension catches both.
Deliverability & Compliance
SPF, DKIM, and DMARC alignment signals. Authentication header completeness. Sender reputation indicators. If your email's technical sending setup has gaps that affect deliverability, this is where they surface.
Accessibility & UI
Alt text coverage on every image. Colour contrast ratios. Font size legibility on mobile viewports. Screen reader compatibility. Accessibility isn't optional — it's also a deliverability signal.
Content & Spam Prevention
Content patterns, keyword density, link-to-text ratios, and structural signals that affect both deliverability and spam classification — beyond what Spam Analysis covers at the rules engine level.
Your email read the way a human recipient would read it.
AI scoring is based on structured evaluation models and real email heuristics — not generic text scoring. Five dimensions of content quality — evaluated against what actually drives email engagement and readability, not just technical correctness.
Sentiment Analysis
Detects the overall emotional tone of your email. Flags content that reads as overly negative, alarmist, or tonally inconsistent with what the email is trying to do.
Tone Detection
Evaluates whether the tone matches the context. A password reset should feel functional. A welcome email should feel warm. A billing alert should be clear and calm. Tone mismatches are flagged with specific locations.
Grammar & Spelling
Comprehensive check across subject line, preview text, and full body. Errors in transactional emails damage trust before the user even reads the content.
Readability Score
Measures sentence length, vocabulary complexity, and overall reading level. Flags emails that are harder to read than they need to be — especially important in transactional contexts where clarity is everything.
Clarity & Conciseness
Evaluates whether your CTA is specific and actionable, your message is focused, and your email doesn't bury the point. Flags weak CTAs and verbose sections that reduce engagement.
Sentiment Analysis
Detects the overall emotional tone of your email. Flags content that reads as overly negative, alarmist, or tonally inconsistent with what the email is trying to do.
Tone Detection
Evaluates whether the tone matches the context. A password reset should feel functional. A welcome email should feel warm. A billing alert should be clear and calm. Tone mismatches are flagged with specific locations.
Grammar & Spelling
Comprehensive check across subject line, preview text, and full body. Errors in transactional emails damage trust before the user even reads the content.
Readability Score
Measures sentence length, vocabulary complexity, and overall reading level. Flags emails that are harder to read than they need to be — especially important in transactional contexts where clarity is everything.
Clarity & Conciseness
Evaluates whether your CTA is specific and actionable, your message is focused, and your email doesn't bury the point. Flags weak CTAs and verbose sections that reduce engagement.
Sentiment Analysis
Detects the overall emotional tone of your email. Flags content that reads as overly negative, alarmist, or tonally inconsistent with what the email is trying to do.
Tone Detection
Evaluates whether the tone matches the context. A password reset should feel functional. A welcome email should feel warm. A billing alert should be clear and calm. Tone mismatches are flagged with specific locations.
Grammar & Spelling
Comprehensive check across subject line, preview text, and full body. Errors in transactional emails damage trust before the user even reads the content.
Readability Score
Measures sentence length, vocabulary complexity, and overall reading level. Flags emails that are harder to read than they need to be — especially important in transactional contexts where clarity is everything.
Clarity & Conciseness
Evaluates whether your CTA is specific and actionable, your message is focused, and your email doesn't bury the point. Flags weak CTAs and verbose sections that reduce engagement.
When to use each score
Before every template release
Run HTML Check and Link Check on every template change before it merges. Make it part of your pre-release checklist — not an afterthought caught in production.
When open rates drop
Low open rates often signal SPF, DKIM, or DMARC issues — not subject line problems. Use Performance Score to check your authentication and sender reputation signals before assuming the copy is at fault.
When emails land in spam
Reproduce the email in Sandbox and check Spam Analysis. The rules triggered tell you exactly what spam filters are reacting to — specific rules, specific weights, specific fixes.
Before shipping a new template
Use AI Score on any new email template before it goes to production. Catch weak CTAs, readability problems, and tone mismatches in staging — not after the email has sent to thousands of users.
Accessibility and regulatory sign-off
Use Performance Score's accessibility dimension to verify alt text coverage, contrast ratios, and mobile legibility — especially if your product serves regulated industries.
The things developers ask about Email Scoring
Which scores run automatically?
HTML Check, Link Check, and Spam Analysis run automatically on every email that arrives — no trigger needed. Performance Score and AI Score are triggered manually from within the inbox.
What rules engine does Spam Analysis use?
SpamAssassin — the same engine used by major email providers. Every triggered rule is listed with its weight and a plain-language explanation of what it flagged.
Can I re-score an email without resending it?
No. Scores are tied to the email as received. Fix the issue, resend the email to your inbox, and the new version scores fresh. This confirms the fix made it into your actual code — not just your notes.
Does HTML Check test against all email clients?
It validates against support data for Gmail, Outlook, Apple Mail, and major mobile clients. Each flagged issue shows which specific clients are affected.
Is AI scoring reliable?
AI scoring uses structured evaluation models and real email heuristics — not generic text analysis. It gives consistent, structured feedback on content quality. It's a tool for catching clear issues — not a replacement for editorial judgement.
Email Inbox is one piece of a complete testing environment
Your app sends emails, SMS, webhooks, and TOTP codes. Sandbox handles all four — in one workspace, under one account, visible to your whole team.
Email Inbox
SMS Inbox
Webhook Inbox
TOTP Inbox
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Test Email, SMS, Webhooks & 2FA codes without touching production.
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