What is Hard Bounce?
A hard bounce is a permanent email delivery failure that occurs when the recipient address is invalid, doesn't exist, or the domain is unreachable—requiring immediate removal from your list.
A hard bounce means your email cannot be delivered now or ever. The receiving mail server returns a permanent failure code (5xx SMTP error), indicating that no amount of retrying will succeed. The address is fundamentally undeliverable.
Common causes of hard bounces include: • The email address doesn't exist (typo like "gmial.com" or the user deleted their account) • The domain doesn't exist or has no mail server configured • The recipient's mail server has permanently blocked your sender • The mailbox has been disabled or abandoned
Hard bounces are different from soft bounces, which are temporary failures. When you see a hard bounce, the address should be removed from your list immediately—continuing to send to it damages your sender reputation and can get you blacklisted.
Most email service providers automatically suppress hard-bounced addresses, but understanding the distinction helps you maintain list quality and diagnose delivery issues.
Why Hard Bounce Matters
Every hard bounce signals to inbox providers that you're not maintaining your list properly. Send to too many invalid addresses and providers start assuming you're a spammer—which tanks deliverability for your entire domain. Industry best practice is keeping your hard bounce rate below 0.5%. Rates above 2% trigger spam filters and can result in blacklisting. For transactional emails, a hard bounce also means a user can't receive critical communications like password resets or order confirmations.
How Ark Handles Hard Bounce
Ark automatically detects hard bounces and adds them to your suppression list in real-time. We never attempt to send to a hard-bounced address again, protecting your sender reputation. Our API returns detailed bounce codes so you can update your user records and notify users of invalid email addresses. The dashboard shows bounce trends to help you identify list quality issues early.
Frequently Asked Questions
What's the difference between a hard bounce and soft bounce?
A hard bounce is permanent—the address will never work and should be removed immediately. A soft bounce is temporary—the mailbox might be full or the server temporarily unavailable. Soft bounces can resolve themselves, but repeated soft bounces (typically 3-7) should be treated as hard bounces.
Should I try sending to a hard-bounced address again later?
No. Hard bounces are permanent failures. Retrying damages your sender reputation because inbox providers see you repeatedly sending to invalid addresses—a classic spammer behavior. Remove hard bounces immediately and permanently.
Why did a previously valid address suddenly hard bounce?
Email addresses become invalid over time. The user may have left a company (work emails get deleted), abandoned a personal account, or the domain may have expired. This is why regular list cleaning is important—about 25% of email addresses become invalid each year.
Can authentication issues cause hard bounces?
Yes. If your SPF, DKIM, or DMARC is misconfigured, some strict mail servers will reject your emails with a hard bounce. Check your authentication setup if you see unexpected hard bounces across multiple domains.
What hard bounce rate is acceptable?
Keep hard bounces below 0.5% of your total sends. Below 0.3% is ideal. Anything above 2% indicates serious list quality problems that will damage your sender reputation. For a clean, well-maintained list, hard bounces should be rare.
Related Terms
Soft Bounce
A soft bounce is a temporary email delivery failure caused by issues like a full mailbox, server dow...
Bounce Rate
Email bounce rate is the percentage of emails that couldn't be delivered to recipients, categorized ...
Suppression List
A suppression list is a database of email addresses that should not receive emails, including bounce...
Email Deliverability
Email deliverability is the ability to successfully deliver emails to recipients' inboxes rather tha...
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