🧠 TL;DR: The Integration Depends on Your Workflow
| Use Case | Recommended Option |
|---|---|
| Signup forms / real-time validation | ✅ API |
| Cold outreach or CRM clean-up | ✅ Bulk upload |
| Marketing automation (eg. Zapier) | Depends |
| Webhooks or product onboarding | ✅ API |
| Legacy list clean-up / migrations | ✅ Bulk |
📱 If your validation happens at runtime
→ Go API
📋 If you're working with large static lists
→ Go Bulk
🔌 What Is an Email Validation API?
An email validation API lets your product or system verify email addresses programmatically:
- • Runs live checks (syntax, MX, SMTP, catch-all)
- • Returns structured JSON (valid / invalid / risky)
- • Can be embedded in any app, form, CRM, or automation
Example use cases:
❌ Block typos at signup
Prevent users from entering invalid emails
⚠️ Flag disposable domains
Before onboarding or trial signup
✅ Enrich leads in real time
Score email quality as data flows
💻 Sample API Integration
Sample Request
GET https://api.lero.email/validate?email=ana@company.com Authorization: Bearer YOUR_API_KEY Content-Type: application/json
Sample Response
{
"status": "valid",
"is_disposable": false,
"is_catchall": false,
"smtp_check": true,
"mx_check": true,
"score": 0.973,
"risk": "low",
"processing_time_ms": 47
}⚡ Lero's API responds in <50 ms—ideal for signup flows where speed matters.
Integration Examples
JavaScript (Frontend)
const validateEmail = async (email) => {
const response = await fetch(
`https://api.lero.email/validate?email=${email}`,
{
headers: {
'Authorization': 'Bearer YOUR_API_KEY'
}
}
);
return response.json();
};Python (Backend)
import requests
def validate_email(email):
response = requests.get(
f"https://api.lero.email/validate",
params={"email": email},
headers={"Authorization": "Bearer YOUR_API_KEY"}
)
return response.json()📁 What Is a Bulk Upload Integration?
Bulk validation means you upload a full list (CSV, XLSX) and Lero returns results once all entries are processed.
Ideal when:
- • You've collected leads through other systems
- • You're cleaning legacy CRMs
- • You want a full snapshot of list quality
Supports millions of emails
Output includes all metadata
No-code via dashboard
💡 Learn more about bulk performance: How Lero Validates 1M Emails in Seconds
⚖️ API vs. Bulk Upload: Side-by-Side Comparison
| Feature | API | Bulk Upload |
|---|---|---|
| Speed | ~50 ms per email | Batch (eg. 10K in 7s) |
| Setup required | Needs integration (dev work) | No-code via dashboard |
| Ideal for | Signup flows, realtime workflows | Cold outreach, CRM cleaning |
| Result format | JSON (realtime) | CSV / XLSX / JSON (batch) |
| Accuracy | 97.3% | 97.3% |
| Price per email | Same in both | Same in both |
🛠️ Technical Implementation Considerations
🔌 API Implementation
✅ Best Practices
- • Cache results for repeated emails
- • Handle rate limits gracefully
- • Use async/await for better UX
- • Implement retry logic
⚡ Rate Limits
- • 1000 requests/minute (free)
- • 10K requests/minute (paid)
- • Burst handling included
📁 Bulk Implementation
✅ File Requirements
- • CSV, XLSX, TXT formats
- • Up to 10M rows per file
- • UTF-8 encoding preferred
- • Header row recommended
⏱️ Processing Time
- • 1K emails: ~7 seconds
- • 10K emails: ~1 minute
- • 100K emails: ~10 minutes
- • 1M emails: ~1.5 hours
🤖 Bonus: Combine Both with Lero
Lero offers the flexibility to use both approaches seamlessly:
🔄 Unified Platform
- • API with 99.9% uptime SLA
- • Bulk dashboard + Zapier + Make
- • Same pricing across both modes
- • Real-time streaming for bulk if needed
🎯 Recommended Stack
- • API for your product/signup forms
- • Bulk for cleaning sales/marketing campaigns
- • Webhooks for automated workflows
- • Analytics to track validation trends
💡 Pro tip: Start with API for real-time needs, then add bulk processing for larger datasets. You can use the same account and credits for both.
📊 Integration Decision Matrix
| Scenario | Volume | Timing | Best Choice |
|---|---|---|---|
| User registration form | 1 at a time | Instant | API |
| Newsletter signup | 1-100/day | Real-time | API |
| CRM data cleanup | 10K-100K | Batch job | Bulk |
| Cold email campaign prep | 1K-50K | Before send | Bulk |
| Lead enrichment pipeline | 100-1K/hour | Streaming | API + Bulk |
| E-commerce checkout | 1-10/minute | Instant | API |
🔗 Related Resources
❓ Frequently Asked Questions
Q1: Can I switch between API and bulk validation?
Yes! Both use the same credit pool and account. You can use API for real-time needs and bulk for larger datasets seamlessly.
Q2: What's the cost difference between API and bulk?
Pricing is identical per email validated. Volume discounts apply regardless of whether you use API or bulk validation.
Q3: How do I handle API timeouts or errors?
Implement exponential backoff retry logic. Our API returns specific error codes to help you handle different scenarios appropriately.
Q4: Can I get real-time progress for bulk uploads?
Yes! Our dashboard shows live progress, and we offer webhook notifications when bulk jobs complete.
Q5: Is there a minimum or maximum file size for bulk uploads?
Minimum 1 email, maximum 10M emails per file. For larger datasets, contact us for enterprise processing options.
🚀 Ready to Choose Your Integration?
Whether you need real-time API validation or bulk processing power, Lero has you covered with the same accuracy and speed.
No credit card required • Same pricing for API & bulk • 97.3% accuracy guaranteed