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No Bounce Handling Causing Sender Reputation Damage
Your application continues to send emails to addresses that have previously bounced (invalid addresses, full mailboxes, blocked domains). This damages your sender reputation score, causing email providers to throttle or block all your emails, including those to valid recipients.
Without bounce handling, your deliverability degrades over time. Emails that used to reach inboxes start landing in spam, then stop arriving at all. By the time you notice, your sending domain may be blacklisted and recovery takes weeks.
The issue compounds because every failed delivery attempt further damages your reputation, creating a downward spiral that affects all your users, not just the ones with invalid addresses.
Error Messages You Might See
550 5.1.1 User unknown
552 Mailbox full
Email suppressed: previously bounced
Sender reputation score: critical
Domain blacklisted by Spamhaus
Common Causes
- No webhook listener for bounces — The email service reports bounces via webhooks but the app has no endpoint to receive them
- Bounced addresses not flagged — Even if bounce notifications are received, the app doesn't mark addresses as invalid in the database
- No distinction between hard and soft bounces — Hard bounces (invalid address) should permanently stop sending, soft bounces (full mailbox) should retry then stop
- Suppression list not checked before sending — The app doesn't check a suppression list before attempting to send each email
- Catch-all sending to user-provided addresses — Newsletter or notification features send to any address without validation
How to Fix It
- Set up bounce webhook endpoint — Create an endpoint to receive bounce notifications from your email provider (SendGrid Event Webhook, Mailgun webhooks, SES notifications)
- Maintain a suppression list — Store bounced addresses in a database table and check it before every send
- Handle bounce types differently — Permanently suppress hard bounces immediately. Retry soft bounces 3 times over 72 hours, then suppress
- Validate email addresses at signup — Use email verification APIs or double opt-in to prevent invalid addresses from entering your system
- Monitor sender reputation — Use tools like Google Postmaster Tools and your email provider's reputation dashboard to track your domain health
Real developers can help you.
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You don't need to be technical. Just describe what's wrong and a verified developer will handle the rest.
Get HelpFrequently Asked Questions
What's the difference between a hard and soft bounce?
A hard bounce means the address is permanently invalid (user doesn't exist, domain doesn't exist). A soft bounce is temporary (mailbox full, server temporarily down). Stop sending to hard bounces immediately; retry soft bounces a few times before suppressing.
How do I recover a damaged sender reputation?
Stop sending to all bounced and unengaged addresses immediately. Clean your list to only active, confirmed recipients. Start sending low volumes and gradually increase. It typically takes 2-4 weeks for reputation to recover.