What is an email hard bounce?

Updated Oct 21, 2026

A hard bounce is an email that can't be delivered because of a permanent problem, most often an email address or domain that doesn't exist. The receiving server rejects the message and returns an error code, usually starting with 5. Unlike a soft bounce, which is temporary, resending the same message to the same address won't work.

Hard bounces matter because mailbox providers watch how often you send to bad addresses. A high hard bounce rate signals a poorly maintained list, which hurts your sender reputation and makes it harder for all your emails, including the ones to valid contacts, to reach the inbox. For the bigger picture, see bounced email.

Hard bounce vs. soft bounce

	Hard bounce	Soft bounce
Problem	Permanent	Temporary
Typical code	5xx (for example, 550 5.1.1)	4xx (for example, 421 or 451)
Common causes	Address or domain doesn't exist, account closed	Mailbox full, server busy or down, sending too fast
Will a retry work?	No	Often, after a delay
What to do	Stop sending to the address	Let your platform retry, and watch for repeat bounces

Common causes of hard bounces

Cause	What happened	Example code
Mailbox doesn't exist	The part before the @ is wrong, misspelled or was never created.	550 5.1.1
Domain doesn't exist	The part after the @ is misspelled (like gmial.com) or the domain no longer exists or accepts email.	550 5.1.2
Account closed or disabled	The person left a company or abandoned the account.	550 5.2.1
Invalid syntax	The address is malformed, such as a missing @ or extra spaces.	553 5.1.3
Message refused	The receiving server blocked the message by policy, for example because of failed authentication or a blocklisting.	550 5.7.1

Codes follow the standard in RFC 3463. Exact wording varies by mailbox provider.

Not every 5xx error means a bad address

A full mailbox (5.2.2) is technically a temporary condition, and the standard says it should be treated that way even when it uses a 5xx code. And policy rejections (5.7.x) usually point to a problem on the sender's side, such as missing SPF, DKIM or DMARC records, a blocklisted IP or a poor reputation. Microsoft, for example, now rejects noncompliant bulk mail with a 550 5.7.515 error. If many valid contacts suddenly hard bounce with 5.7.x codes, fix your authentication and reputation rather than removing contacts.

Why hard bounces hurt deliverability

They damage sender reputation. Mailbox providers see repeated sends to invalid addresses as a sign of purchased, scraped or neglected lists.
They can trigger throttling or blocking. High bounce rates lead providers, and your email platform, to slow or stop delivery.
They can hide spam traps. Old, abandoned addresses are sometimes turned into spam traps, which hurt reputation even more.
They waste sends and skew reporting. Every bounce is a message that never had a chance to be clicked.

What's an acceptable bounce rate?

Bounce rate	What it means
Under 2%	Healthy. Keep up your list hygiene.
2% to 5%	Acceptable, but worth watching.
Over 5%	A problem to fix before your next send.

Bounce rate is the percentage of sent emails that bounced. Track hard bounces separately, since even a small, steady stream of them points to a list quality issue.

How to prevent hard bounces

Use double opt-in so new subscribers confirm their address before you add them. See inbox placement tips.
Validate addresses at signup to catch typos like gmial.com or missing characters.
Never buy or rent lists. They're full of invalid addresses and spam traps.
Verify old or imported lists with a list validation service before sending.
Clean your list regularly and remove contacts who haven't clicked in a long time. See Email list cleaning: The complete guide.
Keep authentication in place with SPF, DKIM and DMARC so policy rejections don't look like bad addresses.
Send consistently. Lists that sit unused for months decay as people change jobs and abandon accounts.

How DailyStory handles hard bounces

When an email hard bounces in DailyStory, the delivery fails permanently and the contact's status changes to Bounced, so you don't keep sending to an address that won't accept mail. Report dashboards show bounce rates for individual emails and for any time frame, and DailyStory throttles delivery if a send produces a high bounce rate, which helps protect your reputation.

To verify addresses before you send, DailyStory integrates with list validation services such as NeverBounce. Learn more in the Bounced Email Guide and the Email FAQ, or explore email marketing features.

Frequently asked questions

Should I delete contacts that hard bounce?

Stop emailing them, but you don't have to delete the contact record. The person may still be a customer you reach by SMS or another channel, or they may give you a new email address later.

Can a hard-bounced address become valid again?

Occasionally, such as when a company fixes a mail server problem. Don't resend on a hunch, though. Ask the contact to confirm their address through another channel or a form, then update it.

Why did a valid email address hard bounce?

Check the bounce code. A 5.7.x code usually means the receiving server refused your message for policy reasons, such as failed authentication, a blocklisted IP or content filtering, rather than an invalid address.

Do hard bounces affect SMS?

Bounces are an email concept. Text messages have their own delivery failures, such as invalid or disconnected numbers and carrier filtering, which you should also remove from your lists.