Menu
Convert Markdown to RFC 5322 email (.eml) with inline CSS and CID images
End-to-end academic paper drafting for CHI, HBR, journals, and conferences with venue-specific templates, drafting workflows, and revision strategies.
Generate on-brand Alex — ACT Edition SVG banners for documents (READMEs, plans, notes, release artifacts)
Patterns for fiction, narrative structure, character development, dialogue, and storytelling craft.
Convert Word documents (.docx) to clean Markdown with image extraction and pandoc cleanup
Greeting-triggered self-check — recognise greetings, check Edition version against the upstream tag, scan AI-Memory announcements, and report inside the greeting reply
Write markdown that passes markdownlint on first attempt — encode the most common rules as muscle memory
| type | skill |
| lifecycle | stable |
| inheritance | inheritable |
| name | md-to-eml |
| description | Convert Markdown to RFC 5322 email (.eml) with inline CSS and CID images |
| tier | standard |
| applyTo | **/*eml* |
| currency | "2026-04-22T00:00:00.000Z" |
| lastReviewed | "2026-04-30T00:00:00.000Z" |
Write in Markdown, send as professional email — works in any email client
Staleness Watch: See EXTERNAL-API-REGISTRY.md for source URLs and recheck cadence
Convert Markdown documents with YAML frontmatter into RFC 5322-compliant .eml files ready for governance, newsletter, and stakeholder communication workflows.
| Format | Status | Notes |
|---|---|---|
| Headings | ✅ | H1-H6 with inline styles |
| Bold/Italic | ✅ | Standard emphasis |
| Links | ✅ | Clickable hyperlinks |
| Images | ✅ | CID embedded as attachments |
| Code blocks | ✅ | Monospace, gray background |
| Inline code | ✅ | Highlighted |
| Tables | ✅ | HTML tables with borders |
| Blockquotes | ✅ | Indented with border |
| Lists | ✅ | Ordered and unordered |
| Mermaid diagrams | ⚠️ | Table fallback (no JS in email) |
| Emoji | ✅ | Unicode preserved |
| Horizontal rules | ✅ | Styled dividers |
| Feature | Details |
|---|---|
| YAML frontmatter | Maps to RFC 5322 headers (To, From, Subject, CC, Reply-To) |
| Email-safe HTML | Inline CSS with table-based layout (no <style> blocks) |
| Mermaid fallback | Diagrams converted to ASCII table representation (email-safe) |
| CID images | Local images embedded as base64 multipart MIME attachments |
| Emoji preservation | Subject and body emoji render correctly across clients |
| Test mode | --test flag overrides recipients for safe preview |
# Basic conversion
node .github/muscles/md-to-eml.cjs newsletter.md
# With test recipient override (safe preview)
node .github/muscles/md-to-eml.cjs newsletter.md --test --test-to me@example.com
# Embed images as CID attachments
node .github/muscles/md-to-eml.cjs update.md --inline-images
# Debug mode (saves intermediate HTML)
node .github/muscles/md-to-eml.cjs update.md --debug
| Option | Default | Description |
|---|---|---|
--test | off | Override recipients for safe preview |
--test-to ADDRESS | frontmatter from | Custom test recipient email |
--inline-images | off | Embed images as base64 CID attachments |
--debug | off | Save intermediate HTML for inspection |
The YAML frontmatter maps directly to RFC 5322 email headers:
---
to: team@example.com
from: sender@example.com
subject: 📊 Weekly Update - Sprint 42
cc: manager@example.com
reply-to: noreply@example.com
---
| Field | RFC 5322 Header | Required | Notes |
|---|---|---|---|
to | To | ✅ | Primary recipient(s), comma-separated |
from | From | ✅ | Sender address |
subject | Subject | ✅ | Supports emoji |
cc | Cc | ❌ | Carbon copy recipients |
reply-to | Reply-To | ❌ | Reply address if different from From |
| Client | HTML | Images | Tables | Emoji |
|---|---|---|---|---|
| Outlook (Windows) | ✅ | ✅ CID | ✅ | ✅ |
| Outlook (Mac) | ✅ | ✅ CID | ✅ | ✅ |
| Gmail (Web) | ✅ | ✅ CID | ✅ | ✅ |
| Apple Mail | ✅ | ✅ CID | ✅ | ✅ |
| Thunderbird | ✅ | ✅ CID | ✅ | ✅ |
| Mobile (iOS/Android) | ✅ | ⚠️ varies | ✅ | ✅ |
--test --test-to your@email.com--test for productionEmail clients cannot execute JavaScript, so Mermaid diagrams are converted to text-based table representations:
┌─────────────────┐
│ Original Mermaid │ → Table Fallback
└─────────────────┘
flowchart LR → | Step | Description |
A --> B | A | Start |
B --> C | B | Process |
| C | End |
For high-fidelity diagrams, pre-render to PNG and include as images.
| Problem | Cause | Solution |
|---|---|---|
| "pandoc not found" | pandoc not installed | winget install pandoc |
| Images not showing | CID not supported | Use --inline-images flag |
| Formatting broken | Client strips styles | Use simpler formatting |
| Large file size | Too many images | Link images instead of embedding |
| Subject truncated | Too long | Keep under 60 characters |
| Emoji not showing | Old email client | Use text alternatives |
markdown-preprocessor.cjs, mermaid-pipeline.cjs.github/muscles/md-to-eml.cjs (v1.0.0)
| Condition | Verdict | Action |
|---|---|---|
| Subject, From, To headers present and correct | Accept | Required fields for valid .eml |
| Missing or malformed email headers | Reject | Check frontmatter extraction |
| HTML body renders in Outlook/Gmail preview | Accept | Test in at least one client |
| Body shows raw HTML tags or broken layout | Reject | Check MIME Content-Type is text/html |
| Inline images display (CID or base64) | Accept | Verify no external URL references |
| Images missing or show broken icons | Reject | Embed as base64 or CID attachment |
| Links are clickable and point to correct URLs | Accept | Spot-check 2-3 links |
| Mermaid diagrams pre-rendered as inline images | Accept | Raw mermaid syntax is not email-safe |
| Mermaid diagrams show as code blocks | Reject | Pre-render to PNG before embedding |
| File opens in default mail client without errors | Accept | Test .eml file import |
| Total .eml size >5MB | Warning | Compress images or link instead of embed |
| Plain-text MIME part included as fallback | Accept | Recommended for accessibility |
Skill version: 2.0.0 | Last updated: 2026-04-14 | Category: document-conversion