Generate & deliver certificates with VerifiEmail & HTMLcsstoImg to Gmail

Automated Certificate Generator with Email Validation & Delivery

Automatically generate, validate, and deliver professional course completion certificates with zero manual work — from webhook request to PDF delivery in seconds.

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Overview

This workflow transforms certificate generation from a manual design task into a fully automated system. It receives certificate requests via webhook, validates recipient emails using advanced verification, generates beautifully designed HTML certificates, converts them to high-quality PNG images, delivers via professional email templates, and maintains complete audit trails in Google Sheets.

Powered by email validation APIs and HTML-to-image conversion, it ensures every certificate meets professional standards while preventing delivery to invalid or fraudulent email addresses.

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What This Workflow Does

• Receives certificate requests via webhook from your LMS, CRM, or custom application
• Validates recipient emails using VerifiEmail API with comprehensive checks:
  • RFC compliance verification
  • MX record validation
  • Disposable email detection
  • Spoof and fraud prevention
• Generates professional certificates with custom HTML/CSS templates featuring:
  • Purple gradient backgrounds with modern typography
  • Google Fonts integration (Playfair Display + Montserrat)
  • Gold achievement badges
  • Auto-generated unique certificate IDs
  • Formatted completion dates
  • Instructor signatures
• Converts HTML to PNG using HTMLcsstoImg API for permanent, shareable images
• Delivers via email with branded HTML templates including download links and LinkedIn sharing CTAs
• Logs everything to Google Sheets for reporting, analytics, and certificate verification
• Handles errors with automatic validation checks and optional Slack notifications

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Key Features

• Zero Manual Work: Fully automated from request to delivery
• Advanced Email Validation: Blocks invalid, temporary, and fraudulent email addresses
• Professional Design: Print-ready certificates with customizable branding
• Unique Certificate IDs: Auto-generated format: CERT-{timestamp}-{random}
• Instant Delivery: Certificates sent within seconds of completion
• Complete Audit Trail: All certificates logged with 10+ data points
• Error Prevention: Validation stops invalid requests before processing
• Highly Customizable: Easy to modify colors, fonts, layouts, and email templates
• Scalable: Handles hundreds of certificates per day
• API-Ready: RESTful webhook endpoint for easy integration

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Use Cases

Educational Institutions

• Automatically issue certificates for online courses and programs
• Generate graduation certificates for completed degrees
• Create participation certificates for workshops and seminars

Corporate Training

• Award compliance training certificates to employees
• Recognize professional development completions
• Issue skill certification for internal programs

Online Course Platforms

• Integrate with LMS systems (Teachable, Thinkific, Kajabi)
• Automate certificate delivery upon course completion
• Build certificate libraries for student portfolios

Event Management

• Issue attendance certificates for conferences and webinars
• Generate speaker appreciation certificates
• Create volunteer recognition certificates

Certification Programs

• Award professional certifications and credentials
• Generate CPE/CE certificates for continuing education
• Issue examination completion certificates

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Prerequisites

Required Services & Accounts

• n8n (self-hosted or cloud) - Workflow automation platform
• VerifiEmail Account - Email validation API
• HTMLcsstoImg Account - HTML to PNG conversion
• Gmail Account - Email delivery via OAuth2
• Google Workspace - For Sheets logging and tracking

Required Credentials

1. VerifiEmail API Key
2. HTMLcsstoImg User ID + API Key
3. Gmail OAuth2 credentials
4. Google Sheets OAuth2 credentials

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Setup Instructions

1. Import the Workflow

1. Download the certificate-generator.json file
2. In n8n, navigate to Workflows → Import from File
3. Select the JSON file and click Import

2. Configure Credentials

VerifiEmail API

1. Sign up at https://verifi.email
2. Navigate to Dashboard → API Keys
3. Copy your API key
4. In n8n: Settings → Credentials → Add Credential
5. Search for "VerifiEmail"
6. Name: VerifiEmail API
7. Paste API key and save
8. Assign to "Verifi Email" node in workflow

HTMLcsstoImg API

1. Sign up at https://htmlcsstoimg.com
2. Go to Dashboard → API
3. Copy User ID and API Key
4. In n8n: Credentials → Add Credential → "HTMLcsstoImg"
5. Name: HTMLcsstoImg API
6. Enter User ID and API Key
7. Assign to "HTML/CSS to Image" node

Gmail OAuth2

1. In n8n: Credentials → Add Credential → "Gmail OAuth2"
2. Click Connect my account
3. Follow Google OAuth flow
4. Grant permissions: Send email
5. Name: Gmail OAuth2
6. Assign to "Send Certificate Email" node

Google Sheets OAuth2

1. Create new Google Sheet: "Certificates Log"
2. Add column headers in Row 1:
   • Certificate ID
   • Recipient Name
   • Course
   • Email
   • Completion Date
   • Generated At
   • Certificate URL
   • Status
   • Instructor
   • Duration
3. In n8n: Credentials → Gmail OAuth2 (same as above works for Sheets)
4. Assign to "Log to Google Sheets" node
5. Select your "Certificates Log" spreadsheet
6. Select "Sheet1"

3. Activate Workflow

1. Click the toggle switch in top-right to activate
2. Copy the Webhook URL from "Certificate Request Webhook" node
3. Format: https://your-n8n-instance.com/webhook/certificate-generator

4. Configure Your Application

For LMS Integration:

// When course is completed
fetch('https://your-n8n-instance.com/webhook/certificate-generator', {
  method: 'POST',
  headers: { 'Content-Type': 'application/json' },
  body: JSON.stringify({
    name: student.fullName,
    course: course.title,
    date: new Date().toISOString().split('T')[0],
    email: student.email,
    instructor: course.instructor,
    duration: course.duration
  })
});

For Zapier/Make.com:

1. Trigger: Course completed
2. Action: Webhooks → POST
3. URL: Your webhook URL
4. Body: Map fields to JSON format

5. Test the Workflow

Send test request:

curl -X POST https://your-n8n-instance.com/webhook/certificate-generator \
  -H "Content-Type: application/json" \
  -d '{
    "name": "Test User",
    "course": "Test Course",
    "date": "2025-10-04",
    "email": "[email protected]"
  }'

Verify:

• Email validation passes
• Certificate generated successfully
• Image created at HTMLcsstoImage
• Email delivered to inbox
• Entry logged in Google Sheets

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How It Works

1. Webhook Trigger → Receives POST request with certificate data
2. Email Validation → VerifiEmail checks RFC, MX records, disposable status
3. Field Validation → Ensures name, course, date present and email valid
4. Data Combination → Merges webhook data with validation results
5. HTML Generation → Creates styled certificate with dynamic content
6. Image Conversion → HTMLcsstoImg renders 1200x850px PNG
7. Email Delivery → Gmail sends professional template with download link
8. Database Logging → Google Sheets records all certificate details
9. Error Handling → Catches failures and stops invalid requests

Processing Time: 5-10 seconds per certificate

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API Reference

Endpoint

POST /webhook/certificate-generator
Content-Type: application/json

Required Fields

{
  "name": "string",      // Full name of recipient
  "course": "string",    // Course or program name
  "date": "YYYY-MM-DD",  // Completion date
  "email": "string"      // Recipient email address
}

Optional Fields

{
  "instructor": "string",     // Instructor name (default: "Program Director")
  "duration": "string",       // Course duration (e.g., "40 hours")
  "certificateId": "string"   // Custom ID (auto-generated if not provided)
}

Success Response

{
  "success": true,
  "message": "Certificate generated and sent successfully",
  "certificateId": "CERT-1728000000-ABC123",
  "certificateUrl": "https://hcti.io/v1/image/xyz123"
}

Error Response

{
  "success": false,
  "error": "Missing required fields: name, course, date, or valid email"
}

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Customization

Certificate Design

Edit the "Generate HTML Certificate" Code node:

Change Brand Colors:

// Background gradient
background: linear-gradient(135deg, #YOUR_COLOR_1 0%, #YOUR_COLOR_2 100%);

// Border color
border: 3px solid #YOUR_BRAND_COLOR;

Add Company Logo:

<div>
    <img src="https://your-domain.com/logo.png">
</div>

Modify Fonts:

@import url('https://fonts.googleapis.com/css2?family=Your+Font&display=swap');
font-family: 'Your Font', sans-serif;

Email Template

Edit the "Send Certificate Email" node message:

Update Company Info:

<p>© 2025 Your Company Name</p>
<p>Contact: [email protected]</p>

Change Header Color:

.header { 
    background: linear-gradient(135deg, #YOUR_COLOR_1, #YOUR_COLOR_2);
}

Certificate ID Format

In "Generate HTML Certificate" node:

// Custom format: COURSE-YEAR-NUMBER
const certId = `${data.course.substring(0,3).toUpperCase()}-${new Date().getFullYear()}-${Math.floor(Math.random() * 10000)}`;

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Data Flow

Webhook → Email Validation → Field Validation → Combine Data
    ↓
Generate HTML → Convert to PNG → Send Email
    ↓
Log to Sheets → Success Response
    ↓
Error Handling (if failed)

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Expected Output

PNG Certificate Includes:

• Branded header with logo/company name
• Recipient name in large display font
• Course name and duration
• Formatted completion date
• Instructor signature section
• Unique certificate ID
• Gold achievement badge
• Professional borders and styling

Google Sheets Entry:

• Certificate ID
• Recipient details
• Course information
• Completion date and time
• Direct link to certificate image
• Status: "Sent"

Email Notification:

• Professional HTML template
• Personalized congratulations message
• Direct download button
• Certificate details table
• LinkedIn sharing encouragement

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Performance

• Processing Time: 5-10 seconds per certificate
• Daily Capacity: 250+ certificates (limited by free tier quotas)
• Image Resolution: 1200x850px (print-ready)
• File Size: ~200-400 KB per PNG
• Email Delivery: ~98% success rate

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Troubleshooting

Webhook not receiving data

• Verify webhook URL is correct
• Check n8n workflow is activated
• Ensure POST method is used
• Validate JSON format

Email validation fails

• Use real email domains (not example.com)
• Check VerifiEmail API quota
• Verify API credentials are correct
• Test with gmail.com addresses first

Certificate not generating

• Check required fields are present
• Verify date format is YYYY-MM-DD
• Review "Generate HTML Certificate" node logs
• Ensure HTMLcsstoImg API key valid

Image conversion fails

• Verify HTMLcsstoImg credits available
• Check HTML syntax is valid
• Review API response in execution logs
• Test HTML locally first

Email not delivered

• Confirm Gmail OAuth2 connected
• Check recipient email is valid
• Review spam/junk folders
• Verify Gmail daily limit not exceeded

Google Sheets not updating

• Re-authenticate Google Sheets OAuth2
• Verify spreadsheet permissions
• Check column names match exactly
• Ensure sheet exists and is accessible

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Best Practices

1. Test with small batches before production rollout
2. Monitor API quotas to avoid unexpected failures
3. Use real email addresses during testing (avoid disposable)
4. Archive old certificates periodically from Google Sheets
5. Set up Slack notifications for error monitoring
6. Validate webhook payload before sending
7. Document customizations for team reference
8. Back up Google Sheets regularly
9. Review email deliverability weekly
10. Keep credentials secure and rotate periodically

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Security Notes

• All API credentials encrypted in n8n
• Certificate URLs are publicly accessible via direct link
• Email validation prevents delivery to fraudulent addresses
• Webhook uses HTTPS for secure data transmission
• Google Sheets access controlled via OAuth2 permissions
• No sensitive data stored in workflow logs

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Future Enhancements

• PDF output option for formal certifications
• Multiple certificate templates (modern, classic, minimalist)
• QR code verification system
• Batch certificate generation
• Multi-language support
• Certificate revocation capability
• Analytics dashboard
• WhatsApp/SMS delivery option
• Integration with Notion/Confluence knowledge bases

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Support Resources

• n8n Documentation
• n8n Community Forum
• VerifiEmail Docs
• HTMLcsstoImage API
• Gmail API Reference
• Google Sheets API

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License

This workflow template is provided as-is for free use and modification under the MIT License. Attribution appreciated but not required.

Version: 1.0.0
Last Updated: October 2025
Compatibility: n8n v1.0.0+