Email bounces occur when messages can't be delivered.

Soft bounces (temporary failures like full inbox, server issues, content blocks) may resolve themselves.

Hard bounces (permanent failures like invalid addresses, typos, closed accounts) require immediate action.

Fix by: Verify email addresses before sending, clean your list regularly, monitor blacklists, check DNS settings (SPF, DKIM, DMARC), avoid spam-like content, and limit daily volume to 200 emails. Use email verification tools and pause campaigns if bounce rate spikes.

Symptoms

Campaign reports show high bounce rate (over 5%)
Emails marked as Bounced in campaign activity
Error codes in bounce messages (550, 554, 421, etc.)
Soft bounce warnings for temporary delivery failures
Hard bounce errors for invalid or non-existent addresses
Recipients report not receiving emails

Environment

Applies to all email campaigns in lemlist. High bounce rates damage the sender's reputation and affect deliverability for future campaigns.

Understanding Bounce Types

Soft Bounce (Temporary)

Causes:

Recipient inbox full
Temporary server problems
Email size limit exceeded
Content blocked by filters
DMARC or antivirus requirements not met
Greylisting or throttling by the recipient server
DNS misconfiguration
Antispam filters are blocking unverified senders

Action: Monitor soft bounces. May resolve automatically, but recurring soft bounces become hard bounces.

Hard Bounce (Permanent)

Causes:

Invalid or non-existent email address
Typos in email address
Outdated addresses or closed accounts
Catch-all domains are rejected after verification
Mailbox deactivated or deleted after verification

Action: Remove immediately to protect the sender's reputation.

Step-by-Step Fix

1. Pause campaigns if the bounce rate is high

If bounce rate exceeds 5%:

Pause active campaigns
Assess damage before sending more emails
Prevents further reputation damage

✅ Verify: Campaigns paused, no more emails being sent

2. Verify DNS authentication settings

Go to your domain DNS provider

Confirm these records are properly configured:

SPF record - Authorizes sending servers
DKIM record - Email signature verification
DMARC record - Policy for failed authentication

Use tools to verify:

MXToolbox DNS lookup
Google Admin Toolbox Check MX

✅ Verify: All three records present and valid

3. Clean email list

Remove or fix:

Hard bounced addresses (invalid/non-existent)
Repeated soft bounce addresses
Addresses with typos (common: gmial.com, yahooo.com)
Inactive addresses (no engagement in 6+ months)

Use the email verification tool before sending:

Verify addresses are deliverable
Remove catch-all and risky addresses
Clean the list before importing to the campaign

✅ Verify: List cleaned, verification tool shows addresses are valid

4. Check blacklist status

Use these tools to check the domain/IP:

MXToolbox Blacklist Check
Spamhaus
Microsoft SNDS (for Outlook deliverability)
Google Postmaster Tools

If blacklisted:

Follow the delisting process for the specific blacklist
Fix the underlying issue (spam complaints, authentication)
Request removal

✅ Verify: Domain and IP not on major blacklists

5. Optimize email content

Avoid spam triggers:

Excessive caps or exclamation marks
Spam phrases ("FREE", "Act now", "Limited time")
Too many links or images
Misleading subject lines
Large attachments

Use spam checker tools before sending

✅ Verify: Spam score low (under 5)

6. Monitor sender reputation

Check reputation using:

Microsoft SNDS (Outlook reputation)
Google Postmaster Tools (Gmail reputation)
Sender Score (overall reputation)

Improve reputation by:

Sending to engaged recipients only
Maintaining a low bounce rate (under 3%)
Avoiding spam complaints
Consistent sending patterns

✅ Verify: Reputation score good (green/high rating)

7. Control email volume

Best practices:

Send a maximum of 200 emails per day per account
Gradually increase volume (warm up)
Spread sends throughout day
Use inbox rotation for larger volumes

✅ Verify: Daily volume within safe limits

Confirm It's Fixed

✓ Bounce rate drops below 5% (ideally under 3%)

✓ Hard bounces removed from list

✓ DNS records (SPF, DKIM, DMARC) verified and valid

✓ Domain not on blacklists

✓ Sender reputation score improving

✓ Test emails deliver successfully

Why It Happens

Bounces occur from invalid addresses, poor list hygiene, DNS authentication issues, spam-like content, or damaged sender reputation. Soft bounces may be temporary (full inbox, server issues) while hard bounces are permanent (invalid addresses). High bounce rates signal to providers that you're sending to bad lists, damaging your reputation.

Prevent this: Verify emails before sending, clean lists regularly, maintain proper DNS authentication, avoid spam content, control sending volume, and monitor reputation.