Email bounces occur when your messages can't be delivered to recipients. Understanding why bounces happen and how to prevent them is critical for maintaining sender reputation and deliverability.
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Two Types of Bounces
Hard Bounces(Permanent Failures)
Hard bounces seriously damage your domain health and sender reputation. Email can't be delivered because:
Email is invalid or doesn't exist
Domain doesn't exist
Email was deleted/deactivated
Typo in email address
Soft Bounces (Temporary Failures)
A soft bounce occurs when the recipient's email address is valid, but the message can't be delivered due to temporary issues.
Key difference from hard bounces: Soft bounces are temporary and may resolve themselves. The same email might be deliverable later.
Common Soft Bounce Causes
Recipient's Inbox Is Full: The recipient's mailbox has reached its storage limit, preventing new messages from being received.
Server Issues: The recipient's email server is temporarily unavailable due to maintenance, overload, or other technical problems.
Poor sender reputation: Issues with DNS records, domain setup, or sending behavior can lead to rejection
Spam Filters: Your emails may be filtered out due to content, keywords, or sender reputation, such as heavy HTML templates, signatures with lots of links/icons, or aggressive sales language.
Copy repetition: When thousands of emails look nearly identical, providers may throttle or defer them as pattern-based outreach.
Links in Step 1: The first email is where providers are strictest. Links in Step 1 can increase soft bounces, especially when combined with repetitive copy.
Sending Too Much, Too Fast: Even with a good setup, sudden volume increases can cause throttling, such as ramping too quickly day over day, large batches in a short time window, or identical emails sent from many inboxes simultaneously
Catch-all domains: Some domains accept all emails initially but reject them later
Blocked Email Address: The recipient's email server may have blocked your email address or domain. Some organizations have strict email policies that block unsolicited emails from unknown senders, causing these messages to bounce.
How to Fix Bounces
Step 1: Review Bounce Notifications
When an email bounces, you'll receive a bounce report in your inbox detailing why delivery failed. These reports typically include error codes and explanations from the recipient's email server, which helps you identify patterns and fix the root cause.
View Bounce Reports Directly in Instantly
To see bounce error messages in Instantly without logging into your email provider, you can enable this setting:
Go to Preferences
Enable the 'Save undelivered emails in Unibox' option
Click "Save"
Once enabled, the bounce notifications from your connected email accounts automatically sync to Unibox.
Step 2: Fix Account Setup
Verify DNS Records (MX, SPF, DKIM, DMARC) Are Properly Set
Go to the Email Accounts dashboard
Click on any account
Click "Test domain setup"
If any records are missing: Learn how to set up DNS records
Ensure Proper Warmup
Minimum warmup requirement: At least 2 weeks before using accounts in campaigns
Daily Sending Limit
Suggested safe limits: 30 cold emails + 10 warmup emails per account per day
Avoid volume spikes
Step 3: Verify Your Leads
Poor lead quality is the common cause of hard bounces.
Verify all leads before launching the campaign
Only contact verified leads
Step 4: Follow Good Sending Practices
Send first emails in plain text without images, links, or attachments.
Add meaningful spintax variation. Spintax only works when it creates real uniqueness, not awkward synonym swaps.
Remove spam triggers using our AI spam words checker
Set up Custom Tracking Domain if you're tracking opens or clicks.
Step 5: Resume Gradually
Start with lower sending volume
Gradually increase sending limits
Continue warmup alongside campaigns