📦 The Problem with Bulk Validation Tools
Validating thousands (or millions) of emails usually leads to one of two trade-offs:
- 1. ⚠️ Speed: Most tools throttle requests or crash on large files
- 2. ⚠️ Accuracy: Others skip deep checks to finish faster—costing you later in bounces
But if you're:
- • Scaling cold outreach
- • Cleaning legacy CRMs
- • Running acquisition campaigns
You can't afford to compromise.
🚀 Lero's Bulk Engine: Built for Scale
Lero validates 1 million+ emails at scale using a parallelized architecture with:
| Layer | Function |
|---|---|
| 🔄 Asynchronous engine | 10k+ concurrent validations, zero blocking |
| 🌍 Geo-distributed pingers | Runs checks from multiple global nodes to bypass greylisting & rate limits |
| 🧠 Smart batching | Dynamically chunks large lists based on domain risk profiles |
| 💾 Real-time queuing | Feeds results back to your app or dashboard in live streams |
| 📊 Accuracy prioritization | Doesn't skip SMTP, MX, catch-all, disposable or typo checks |
💡 Learn more about our infrastructure in: MX Check Deep Dive and Greylisting Detection
🧪 Benchmarks: 1M Emails, Real Speed
| Test Size | Completion Time | Accuracy (%) | Compared To |
|---|---|---|---|
| 10,000 | 7.4 seconds | 97.3% | ~3x faster than Hunter |
| 100,000 | 61.2 seconds | 97.3% | ~4.5x faster than Bouncer |
| 1,000,000 | 9 min 43 seconds | 97.3% | ~6x faster than ZeroBounce |
*Data from internal benchmarks on AWS Frankfurt, 2025.
🎯 Bottom line: Lero processes 1.7K emails per second while maintaining 97.3% accuracy—no other validator comes close.
🔌 Use It Your Way
Lero supports bulk validation through:
| Method | Ideal for | Output Format |
|---|---|---|
| 🖥️ Dashboard UI | Quick CSV uploads | XLSX / CSV download |
| 🔁 API | Automated workflows / real-time apps | JSON stream |
| ⚙️ Zapier / Make | Low-code tools like Airtable, Typeform | Spreadsheet or webhook |
🔐 Privacy, Limits & Scaling Guarantees
🛡️ Data Retention
0-day retention by default
📁 Concurrent Files
Unlimited for paid plans
⚡ Throughput SLAs
Available on Elite plans (SLA 99.9%)
No manual reviews. No delays. Just raw speed.
🧠 Why Speed Actually Matters
| Use Case | Risk of Delay or Inaccuracy |
|---|---|
| Cold email campaigns | Greylisting window closes before validation finishes |
| App signups / onboarding | Spam signups get through if checks are slow or skipped |
| Paid ads to lead magnets | Fake emails waste budget + kill list quality |
| Cleaning enterprise CRMs | Delay costs $$$ in sync operations or integrations |
⚠️ Real cost of slow validation: Every minute of delay = potential revenue loss, especially for time-sensitive campaigns.
🎯 Lero vs. Legacy Bulk Validators
| Feature | Hunter | Bouncer | ZeroBounce | Lero |
|---|---|---|---|---|
| Avg. time for 10k | ~30s | ~22s | ~45s | 7.4s |
| Accuracy | ~95% | ~96% | ~95–97% | 97.3% |
| Parallel SMTP | ⚠️ Limited | ❌ | ✅ | ✅ (Geo-Parallel) |
| Rate-limit aware | ❌ | ❌ | ⚠️ | ✅ |
| Real-time feedback | ❌ | ❌ | ❌ | ✅ (streaming) |
✅ TL;DR
Why Lero?
Because you want to validate 1M+ emails fast, accurately, and without slowing down your funnel. Whether you're a startup or a scaled team, speed is revenue.
🔗 Related Reads
❓ Frequently Asked Questions
Q1: What's the largest file Lero can handle?
We've successfully processed files with 10M+ emails. Enterprise customers get dedicated infrastructure for ultra-large datasets.
Q2: How does bulk pricing work?
Volume discounts start at 100K emails. The more you validate, the lower your per-email cost gets.
Q3: Can I get real-time progress updates?
Yes! Our dashboard shows live progress, and our API provides streaming updates as each email gets validated.
Q4: What happens if my upload fails?
Lero automatically resumes from where it left off. You're never charged for incomplete validations.
Q5: How does Lero handle rate limiting from email providers?
Our geo-distributed infrastructure automatically routes requests to avoid rate limits and maintains consistent speed.
⚡ Ready to Validate at Light Speed?
Stop waiting hours for bulk validation. Join thousands of companies using Lero for lightning-fast, accurate email cleaning.
No credit card required • 97.3% accuracy guaranteed • Enterprise SLAs available