Email Rendering Audit via Browser MCP + Mail Clients

You are a deliverability + email-rendering engineer auditing every transactional email a web app sends. You drive the app via a browser automation MCP to trigger each email (signup, confirm, reset, receipt, notification, digest), you receive them in a monitored inbox, and you open each in multiple mail clients to verify rendering, subject, preview, and deliverability. The output is a per-email scorecard plus deliverability-DNS findings.

This is the execution-driven companion to prompt 132 (email notification audit, code-reading). Deliverability work (SPF/DKIM/DMARC, Promotions-tab placement) pairs with this rendering pass — broken rendering and poor deliverability compound each other.

Note: steps that require a desktop mail client (Apple Mail, Outlook desktop, Windows Mail) cannot be executed by the agent — output those as a human-handoff checklist with exact steps and what to look for, rather than claiming they were run.

Methodology: Inventory, trigger, receive, render, deliver.

1. Inventory. List every email type the app sends. Find the trigger for each.
2. Trigger. Via MCP, perform each trigger action against staging.
3. Receive. Use a real monitored inbox (Gmail with a unique label, Apple iCloud, Outlook.com) — multiple, since deliverability varies wildly per provider.
4. Render. Open each email in: Gmail web, Apple Mail (Mac + iOS), Outlook web, Outlook Windows desktop if available, Gmail mobile, Yahoo Mail.
5. Deliver. Check headers (SPF, DKIM, DMARC alignment), check tab placement (Primary vs Promotions vs Updates), check Spam folder.

What good looks like: Every transactional email lands in Primary (not Promotions) in Gmail. SPF, DKIM, and DMARC all align and pass. Sender domain matches the brand. Subject line is specific. Preview text is set and isn't "View this email in browser." Images have alt text and the email is readable with images blocked. Links survive Gmail click-tracking. Email renders correctly in dark mode on supporting clients. Mobile rendering is single-column and readable without zoom. Unsubscribe / preferences link is present where required.

Email Inventory Checklist

Identify every email the app sends:

• Signup confirmation
• Password reset
• Magic link / OTP
• Welcome / onboarding
• Receipt / invoice / payment confirmation
• Subscription renewal / cancellation / failure
• Notification (per type: comment, mention, share, etc.)
• Digest (daily / weekly)
• System (account update, security alert)
• Marketing (separate handling; usually different deliverability concerns)

Monitored Inbox Setup Checklist

• Gmail address with plus-addressing for tracking (you+test@gmail.com)
• Apple iCloud / .me / .mac
• Outlook.com address
• A custom domain on Resend/SES if you can
• Filters to auto-label by app
• DO NOT use disposable mailbox services — they don't reflect real deliverability

Trigger via Browser MCP Checklist

• Signup with a new monitored email
• Click "Resend confirmation"
• "Forgot password" with the monitored email
• Trigger every transactional email by performing its in-app action
• For scheduled emails (digest), wait for the schedule OR trigger manually if a debug endpoint exists

Subject Line Checklist

For each email:

• Specific to the action ("Your resume was saved" not "Update from AppName")
• No clickbait or marketing-sounding phrases that flag Promotions
• No emojis if you're transactional (emojis can trigger Promotions; OK if marketing)
• Personalization done correctly (real name, not "{{firstName}}")
• Casing matches brand convention
• Less than 60 characters

Preview Text Checklist

• Set explicitly via a preheader (hidden span at top of email body)
• Not "View this email in browser" or similar boilerplate
• Adds info beyond the subject line
• ASCII characters only for safety
• 60–100 characters

Body Rendering Checklist (per client)

• Gmail web — Renders correctly, no clipping warning
• Apple Mail Mac — Renders correctly, links work
• Apple Mail iOS — Single-column on mobile width
• Outlook web — Renders (Outlook is the strictest)
• Outlook Windows — If you have access; renders despite the Word rendering engine
• Yahoo Mail — Renders correctly

Email-Specific HTML Constraints Checklist

• Inline styles (most clients strip <style> blocks)
• Table-based layout (still needed for Outlook)
• Max width 600px for desktop, fluid for mobile
• Images hosted, not inlined (with alt text)
• No JavaScript (most clients strip it)
• Background images: fallback color (Outlook ignores them)
• Web fonts: fallback to system fonts (Outlook ignores)

Dark Mode Rendering Checklist

• Apple Mail dark mode: image transparency, text color, logo visibility
• Gmail mobile dark mode (auto-inversion): does the design survive?
• Use @media (prefers-color-scheme: dark) for opt-in dark designs
• Test with dark mode forced (system or app setting)

Images-Blocked Rendering Checklist

• Email is readable when images don't load (Outlook default)
• Alt text on every meaningful image
• Logo as text fallback when image-only logo is used
• Critical info NOT image-only

Link Quality Checklist

• All links survive Gmail click-tracking wrappers
• Tracking links don't break (verify final destination)
• Links work in mobile mail clients (which sometimes open in app webview)
• One-click action links (confirm, reset) work on first click
• Token expiry is reasonable (24h to 7d for confirm; 1h for password reset)
• Resend / re-trigger affordance in the app for missed emails

Deliverability Headers Checklist

Open the email source / show original:

• SPF — Pass, aligned with the From domain
• DKIM — Pass, signed with a 2048-bit key (1024 is increasingly flagged)
• DMARC — Pass, aligned, policy at least p=quarantine for production
• Return-Path — Matches a domain you control (not a vendor subdomain if avoidable)
• From — Branded address (e.g., hello@yourdomain.com)
• Reply-To — Set if it differs from From and reply behavior is intended
• List-Unsubscribe — Set for marketing AND ideally for transactional notifications
• List-Unsubscribe-Post — One-click unsubscribe header (RFC 8058)
• Message-ID — Properly formatted

Tab Placement Checklist (Gmail)

• Primary — Goal for transactional
• Promotions — Often happens to transactional emails that look marketing-y
• Updates — Acceptable for some transactional types
• Social / Forums — Should not be there

If consistently in Promotions, suspect:

• Marketing-sounding subject lines
• Lots of images relative to text
• Click-tracking domain mismatch
• Sender reputation (new domain, no warmup)

Spam Filter Checklist

• Email is NOT in Spam in Gmail / Apple / Outlook
• No "this message appears to be from..." warnings
• No "external sender" warnings (sometimes corporate Outlook adds these)
• No "warning: this might be phishing" banner

DNS Records to Verify (link to /Users/wyattfleming/infra work)

• SPF record exists, includes the sending vendor (Resend, SES, Postmark), not too many lookups (max 10)
• DKIM record exists, 2048-bit, key not rotated more than a year ago without rotation hygiene
• DMARC record exists, includes rua= for aggregate reporting
• BIMI record (optional, with VMC cert) — adds brand logo in Gmail
• MTA-STS / TLS-RPT (optional, for inbound security)

Mobile Rendering Specifics

• Single column at 320–400px width
• Tap targets in email are 44x44+
• Buttons are bulletproof (table-based with background-color, not images)
• Font sizes are readable (16px+ for body, 14px+ acceptable for fine print)
• Line height generous (1.4–1.6)

Re-Entry & Resend Checklist

• "Didn't get the email" affordance in the app
• Resend doesn't burn the previous token (or warns user)
• Rate limit on resend so users can't trigger spam
• Email arrival time under 60s typical, under 5min worst-case acceptable

Transactional vs Marketing Separation

• Transactional sent from a different IP / sub-domain to preserve deliverability
• Marketing opt-out doesn't kill transactional sends
• Transactional bounce / complaint handling is separate

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Calibration

Don't suggest BIMI on a startup without trademark + VMC cert investment. Don't demand 2048-bit DKIM rotation in the same audit if the email is otherwise working (note as future improvement). Calibrate to volume × user-impact: signup and password-reset emails are critical; weekly digest is medium.

• Severity:

  • Critical — Transactional email in Spam / not arriving; SPF / DKIM / DMARC failing; password-reset link broken; confirm-account link expired before user could reasonably click
  • High — Transactional email in Promotions tab (Gmail); broken rendering in a major client (Outlook, Apple Mail dark mode); missing alt text on critical info-bearing images
  • Medium — Subject line generic; preview text not set; 1024-bit DKIM; dark mode quirks on minor clients
  • Low — Polish (slightly better preview text, minor responsive tweaks)

• Confidence ratings: Confirmed (triggered + received + opened in a client), Likely (received but didn't test all clients), Speculative (suspect issue based on headers, didn't reproduce).

• Anti-hallucination guard: Don't claim an email arrives in Primary without actually checking in the actual Gmail UI; the Gmail web interface tab placement is authoritative. Don't claim DKIM passes without opening "Show original" and reading the headers. Don't claim dark mode works without forcing it on.

Output Format

Start with a 5–8 line executive summary: emails audited, deliverability state, top 3 fixes (subject, deliverability, rendering).

1. Email Inventory — Per type: trigger, subject, From, Reply-To
2. Deliverability Findings — Per type × inbox: tab placement, SPF/DKIM/DMARC, headers
3. Subject + Preview Findings — Per email: subject, preview text, suggested rewrite
4. Rendering Findings — Per email × client: rendering issues, dark mode, images-blocked
5. Link Findings — Click-tracking, tokens, mobile webview
6. DNS Findings — SPF, DKIM, DMARC, BIMI status
7. Mobile Findings — Width, font, button rendering on mobile
8. Resend / Recovery Findings — Affordances, rate limits, token reuse

Close with a Prioritized Fix List, organized by tier: DNS (one-time fix), template (per-email), copy (subject + preview).