Learning Objective
By the end of this guide, you'll know how to connect Bouncer with lemlist, verify email lists to identify undeliverable addresses, and automatically remove bad emails from campaigns to improve deliverability and engagement rates.
Why This Matters
Email verification protects your sender reputation and improves campaign performance. Sending to invalid, bounced, or undeliverable emails damages your domain reputation, causes inbox providers to flag your emails as spam, and reduces overall deliverability. Bouncer identifies bad emails before you send—keeping your lists clean, bounce rates low, and engagement rates high.
Prerequisites
Before you start:
Active lemlist account with admin access
Active Bouncer account
Campaign with leads in lemlist ready to verify
API access enabled in lemlist
What Bouncer Does
Bouncer is an email verification service that identifies undeliverable emails in your lists.
With Bouncer + lemlist, you can:
Verify email lists - Check which emails are valid, invalid, risky, or undeliverable before sending
Identify bad emails - Find catch-all, disposable, role-based, and syntax-invalid addresses
Remove undeliverables automatically - Delete bad emails from lemlist campaigns with one click
Protect sender reputation - Prevent bounces that damage domain reputation and deliverability
Improve engagement rates - Send only to valid emails, increasing open and reply rates
Export clean lists - Download verified lists for use across platforms
💡 Recommended timing: Verify lists before launching campaigns or regularly for ongoing list maintenance.
How Bouncer Works with lemlist
Verification flow:
Create campaign and add leads in lemlist
Connect Bouncer to lemlist via API
Select lemlist campaign in Bouncer for verification
Bouncer checks all email addresses
View verification results (deliverable, undeliverable, risky, unknown)
Remove undeliverable emails from lemlist campaign with one click
📚 Reference: Bouncer's article and tutorial video for detailed explanation
Step 1: Generate API Key in lemlist
Access API settings
In lemlist, click your profile (bottom-left), then select Settings
In Settings, go to Integrations, then click Generate in the API overview
Generate and copy API key
In the “Generate a new API key” window, (optionally) enter a name for your API key, then click Create Key
Copy API key immediately (long string of characters)
Store securely in password manager or secure location
⚠️ Critical: You can only view API key once after generation. If you lose it, must generate new key and update in all connected apps (including Bouncer).
💡 Security: Keep API key private. Anyone with your API key can access your lemlist account.
Step 2: Connect Bouncer to lemlist
Access Bouncer integrations
Log in to your Bouncer account
Navigate to Integrations section
Find lemlist in integrations list
Click lemlist configuration or Connect
Add lemlist API key
In lemlist configuration dialog, find API Key field
Paste lemlist API key (copied from Step 1)
Click Save or Connect
✅ Result: Bouncer now connected to lemlist and can access your campaigns.
Step 3: Import Leads to lemlist Campaign
Create campaign and add leads
Before verifying, leads must be in lemlist campaign:
In lemlist, create new campaign or open existing one
Go to Leads section
Click Import New Leads
Choose import method:
CSV upload
CRM import (HubSpot, Salesforce, Pipedrive)
Google Sheets
Manual entry
Import leads to campaign
💡 Verification timing: Best to verify before launching campaign (leads in "To Launch" status).
Step 4: Verify Email List in Bouncer
Start verification
In Bouncer dashboard, go to Verify List
Select lemlist configuration as source
Bouncer displays your lemlist campaigns in dropdown
Select campaign and process
Choose lemlist campaign to verify from dropdown
Review lead count to verify correct campaign selected
Click Process or Start Verification
Bouncer begins checking all email addresses in campaign
⏱️ Processing time: Depends on list size. Small lists (100 emails) verify in minutes. Large lists (10,000+) may take 30+ minutes.
Verification process
What Bouncer checks:
Syntax validation - Email format correct ([email protected])
Domain verification - Domain exists and accepts email
Mailbox verification - Specific mailbox exists and active
Catch-all detection - Identifies domains accepting all emails
Disposable detection - Flags temporary email services
Role-based detection - Identifies generic emails (info@, sales@, admin@)
Verification results:
Deliverable - Valid, safe to send
Undeliverable - Invalid, will bounce
Risky - Catch-all or unknown, may bounce
Unknown - Cannot verify (server timeout, greylisting)
Step 5: Review Verification Results
View results in Bouncer
After processing completes:
Bouncer displays verification summary
Results show:
Total emails verified
Deliverable count (green)
Undeliverable count (red)
Risky count (yellow)
Unknown count (gray)
Click Export to view detailed results
Detailed results
In detailed view:
Email address - Each email in list
Status - Deliverable, undeliverable, risky, unknown
Reason - Why email marked as undeliverable (invalid syntax, mailbox doesn't exist, domain invalid, etc.)
Other data - Catch-all, disposable, role-based indicators
💡 Decision making: Deliverable = safe to send. Undeliverable = remove. Risky = decide based on risk tolerance. Unknown = recheck or decide based on value.
Step 6: Remove Undeliverable Emails from Campaign
Auto-remove bad emails
Critical step to protect deliverability:
In Bouncer verification results, click Export button
Click Remove Undeliverable button
Bouncer automatically removes undeliverable emails from lemlist campaign
Confirmation message appears
⚠️ Permanent action: Removed leads deleted from campaign. Cannot undo. Export list first if you want backup.
Verify removal in lemlist
Return to lemlist campaign
Go to Leads section
Check lead count decreased
Undeliverable emails no longer in campaign
✅ Result: Campaign now contains only deliverable (and optionally risky/unknown) emails. Safe to launch.
Step 7: Export Clean List (Optional)
Download verified list
To use verified list elsewhere:
In Bouncer results, click Export
Choose export format:
All results - Full list with statuses
Deliverable only - Clean list ready to use
Undeliverable only - Bad emails for reference
Select file format (CSV, XLSX)
Download file
💡 Use cases: Import clean list to CRM, use in other email platforms, keep backup of verified data.
Best Practices
Verify before launching campaigns - Check lists before sending to prevent bounces from the start
Verify new lists immediately - Always verify purchased lists, scraped data, or lists from external sources
Re-verify old lists - Email validity changes over time. Re-verify lists older than 3-6 months.
Handle risky emails strategically - For warm outreach (existing relationships), include risky emails. For cold outreach, consider removing to maximize deliverability.
Remove undeliverables immediately - Don't wait. Bad emails in campaign damage sender reputation even if not sent yet.
Monitor bounce rates - If campaign bounce rate exceeds 3-5% after verification, re-verify list or check data source quality.
Keep API key secure - Store in password manager. Regenerate if compromised. Update in Bouncer after regeneration.
Export results for records - Download verification reports to track list quality over time
Verify regularly for ongoing campaigns - If continuously adding leads, verify batches periodically
Don't send to unknown status - If maximizing deliverability critical, remove unknown emails along with undeliverables
Understanding Email Statuses
Deliverable (green)
What it means: Email is valid, mailbox exists, safe to send
Action: Keep in campaign
Example: [email protected] verified with active mailbox
Undeliverable (red)
What it means: Email is invalid and will bounce
Reasons:
Invalid syntax (john@company)
Domain doesn't exist ([email protected])
Mailbox doesn't exist ([email protected] but no john.smith mailbox)
Action: Remove from campaign immediately
Risky (yellow)
What it means: Email may be valid but has risk factors
Reasons:
Catch-all domain (accepts all emails, can't verify specific mailbox)
Disposable email (temp-mail.com, 10minutemail.com)
Role-based email (info@, admin@, sales@)
Action: Decide based on campaign type:
Cold outreach: Consider removing to maximize deliverability
Warm outreach: Keep if relationship established
High-value leads: Keep but monitor engagement
Unknown (gray)
What it means: Cannot verify due to technical issues
Reasons:
Server timeout (mail server didn't respond)
Greylisting (temporary rejection by mail server)
Firewall blocking verification requests
Action:
Conservative: Remove to be safe
Moderate: Re-verify after 24 hours
Aggressive: Keep but monitor closely
Troubleshooting
Can't connect Bouncer to lemlist
Fix: Verify API key copied correctly from lemlist (no extra spaces). Check API key generated successfully (not placeholder text). Ensure using correct lemlist account. Regenerate API key if needed and try again.
Campaign not appearing in Bouncer dropdown
Fix: Verify Bouncer connected to lemlist successfully (check connection status). Refresh Bouncer page. Check campaign exists and has leads in lemlist. Reconnect Bouncer to lemlist if persists.
Verification stuck or not processing
Fix: Check Bouncer account has sufficient credits for verification. Refresh page after 2-3 minutes. For large lists (5,000+ emails), allow more processing time. Contact Bouncer support if stuck over 1 hour.
"Remove Undeliverable" button not working
Fix: Verify Bouncer still connected to lemlist (API key not regenerated). Check you're viewing correct verification results (matches lemlist campaign). Refresh Bouncer page. Manually remove leads in lemlist if button fails.
Leads not removed from lemlist campaign
Fix: Verify clicked "Remove Undeliverable" button in Bouncer. Check API connection still active. Refresh lemlist campaign page. Wait 1-2 minutes for sync. Contact Bouncer support if leads still present.
High percentage of risky/unknown emails
Cause: List quality poor, or verification encountering technical issues.
Fix: Check data source quality. For high unknown percentage, re-verify after 24 hours (may be temporary server issues). Consider using different data source if consistently poor quality.
Lost API key and need to reconnect Bouncer
Fix: In lemlist Settings → Integrations → API, generate new API key. Copy immediately. In Bouncer Integrations → lemlist configuration, update with new API key. Save connection. Test by starting verification.
Verification results don't match expectations
Issue: Expected more deliverable or fewer undeliverable emails.
Fix: Email validity changes frequently. Results reflect current state, not when list created. Check specific undeliverable reasons in Bouncer to understand issues. Review data source quality if many syntax errors or invalid domains.
Important Notes
⚠️ API key view-once: After generating API key in lemlist, you can only view it once. If you leave page, cannot view same key again. Must regenerate new key if lost.
⚠️ Update everywhere after regeneration: If you generate new API key (because old one lost), must update in Bouncer and all other connected apps. Old integrations fail until updated.
⚠️ Removal is permanent: When you click "Remove Undeliverable" in Bouncer, leads permanently deleted from lemlist campaign. Export backup first if needed.
⚠️ Verification uses credits: Bouncer charges credits per email verified. Check credit balance before verifying large lists.
⚠️ Re-verify old lists: Email validity changes over time. Lists older than 3-6 months should be re-verified before use.
⚠️ Bounce rate target: Keep bounce rate under 3-5% to protect sender reputation. If exceeds this after verification, investigate data source quality.