What is a bounced email?

Bounced email

A bounced email is a message that gets rejected by a mail server and returned to the sender. When an email bounces, it means the message never reached the recipient's inbox.

Every bounce generates an automated notification called a Non-Delivery Report (NDR) or Delivery Status Notification (DSN). This report tells you why delivery failed and helps you decide what to do next.

Hard bounce vs. soft bounce

Not all bounces are equal. The type determines whether you should retry or remove the address.

Hard bounces are permanent failures. The email address doesn't exist, the domain is invalid, or the recipient's server has blocked you outright. These addresses should come off your list immediately. Continuing to send to them damages your sender reputation and signals to inbox providers that you don't maintain clean lists.

Soft bounces are temporary problems. The recipient's mailbox might be full, their server might be down, or your message might be too large. Most email service providers will retry soft bounces automatically. If the same address soft bounces repeatedly across multiple campaigns, treat it as a hard bounce and remove it.

Common causes of bounced emails

Bounces happen for specific, diagnosable reasons. Understanding the cause helps you prevent future delivery failures.

• Invalid email address: Typos, outdated addresses, or accounts that no longer exist
• Full mailbox: The recipient has exceeded their storage quota
• Server issues: Temporary outages or configuration problems on the receiving end
• Message blocked: Content triggered spam filters or failed authentication checks
• Size limits: Attachments or images pushed the message beyond the server's maximum
• Authentication failures: Missing or misconfigured SPF, DKIM, or DMARC records

The bounce code in your NDR tells you exactly which issue caused the failure. Codes starting with 5 indicate permanent problems, while codes starting with 4 mean temporary issues worth retrying.

How bounces affect deliverability

Your bounce rate directly influences whether inbox providers trust you. A high bounce rate tells Gmail, Yahoo, and others that you're sending to outdated or purchased lists, and they respond by routing more of your mail to spam or blocking it entirely.

The damage compounds over time. Each bounce chips away at your sender reputation, and once that reputation drops, even your messages to valid, engaged subscribers start landing in junk folders.

Keeping your bounce rate below 2% protects your ability to reach the people who actually want to hear from you.

How to reduce bounced emails

1. Use double opt-in to confirm addresses before adding them to your list. This catches typos and fake submissions at the source.
2. Clean your list regularly by removing addresses that haven't engaged in 6-12 months. Dormant addresses often become invalid.
3. Authenticate your sending domain with SPF, DKIM, and DMARC. Proper authentication prevents policy-based rejections.
4. Monitor your bounce reports after every send. Look for patterns like specific domains rejecting your mail or sudden spikes in failures.
5. Never purchase email lists. Bought lists contain outdated addresses, spam traps, and people who never agreed to hear from you.

What to do when an email bounces

For hard bounces, remove the address from your list with no exceptions. Sending again won't work and will hurt your reputation.

For soft bounces, wait and let your email platform retry. If the same address bounces across three or more campaigns, remove it. A consistently full mailbox usually means an abandoned account.

When you see bounces related to spam filtering or content blocks, review your message. Check for excessive images, suspicious links, or language that triggers filters, then adjust and resend to a test segment before rolling out to your full list.

FAQs

What's a normal bounce rate?
Aim for under 2%. Anything above that signals list quality issues that need attention.

Should I delete all bounced emails?
Delete hard bounces immediately. For soft bounces, give them a few chances before removing. If someone soft bounces three times in a row, treat it as permanent.

Can I prevent all bounces?
No. Some bounces are unavoidable, like when someone leaves a company and their email gets deactivated. The goal is minimizing preventable bounces through good list hygiene and proper authentication.

How do I know if a bounce is hard or soft?
Your email platform categorizes bounces automatically. You can also check the bounce code: 5xx codes are hard bounces, while 4xx codes are soft bounces.

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