Why Do Emails Bounce? Soft Bounce vs Hard Bounce in Email Marketing

Gabriella Walling
Jan 22
5 min read

When an email bounces, you’ll receive a notification saying something like, “Your email to name@domain.com cannot be reached … bounce code 450 4.2.1.” The bounce code given to you in these emails are often very insightful -- if you know what they mean and how to interpret them.

The messaging will depend on your email provider (Mailchimp, Constant Contact, etc.), but they generally fall into two categories: hard bounces and soft bounces. This guide explains the types of bounces, which will help email marketers and sales teams diagnose delivery issues and take actions to maintain a healthy email list.

Definition: What Does Bounced Email Mean?

The meaning of bounced email is, simply, an electronic mail message that didn't reach your intended recipient.

Bounce rate refers to the percentage of email messages that bounce back, or don't go through. This begs the question, “So, what's a good bounce rate for email, then?” Generally, an email bounce rate of less than 2% is considered success. A Mailchimp study (updated in 2023) broke down bounce rates by industry, which can help you understand benchmarks for your industry. In architecture and construction, for example, hard vs soft bounce rates are .53% and 1.54% respectively.

Bounce codes typically fall in 2 categories: hard bounce and soft bounce. You'll find definitions for them online, but remember: bounce code definitions can vary between email service providers, and not all bounce messages include codes, which can be frustrating when you're trying to troubleshoot.

What Does It Mean When an Email Hard Bounces?

Hard bounces are defined as a permanent email failures. You likely cannot resend because the address is bad or the server has blocked the message. Typically, the reason for bouncing has to do with the recipient's address.

Examples of email hard bounces:

Invalid recipient address: The email address does not exist or is not valid (check for typos!). An email recipient's address comprises the entirety of the email: name@domain.com.
Domain not found: The recipient's email domain does not exist. The domain is the string of characters that appear after the @ symbol, as in @gmail.com, @yahoo.com, @yourcompany.com, etc.
Email server rejection: The recipient's email server refuses to accept the email.
Recipient email server block: The recipient's email server blocks the incoming email.
Email content issues: Content-related issues such as size or format that prevent successful delivery.

Hard bounces are typically a 500 bounce code, or a bounce code that starts with a 5 such as 5.0.0 or 5.5.2. See Google's list of Gmail SMTP errors and codes.

Email bounce codes can be tricky to decipher, but following a few best practices can help avoid and reduce your bounce rates. See our guide to avoiding email spam.

What Are Soft Bounces in Email?

The definition of soft email bounce is a temporary failure to deliver an email. You'll likely be able to send it again. Causes include servers being down and recipients' emailboxes being full. Persistent soft bounces may eventually turn into hard bounces, so you'll want to monitor and manage both types.

Examples of email soft bounces:

Mailbox full: The recipient's mailbox is full and cannot receive more emails.
Temporary server issues: Temporary problems with the recipient's email server prevent delivery.
DNS resolution failure: Difficulty in resolving the domain name system (DNS) for the recipient's email server.
Insufficient system storage: Similar to a mailbox being full, this indicates a temporary lack of storage.
Grey-listing: A temporary delay imposed by the recipient's mail server to verify the legitimacy of the sender.

Soft bounces are typically a 400 bounce code, or a bounce code that starts with a 4 such as 4.0.0 or 4.2.1.

How Do You Manage Bounced Emails?

All the info above is great, but what do you do when you get a bounce notification? First of all, don't panic over bounced emails; everyone experiences some undelivered emails because of all the reasons we've listed above (soft vs hard bounces).

You may have heard that ISPs (internet service providers) will block known email domains that send excessive spam. If you are doing legit prospecting and outreach, following B2B email best practices, you don't need to worry about being blacklisted or gray listed by email servers. Don't panic if you have a few bounced emails -- this is normal.

The good news is that many modern email marketing platforms have built-in technology that automates the email validation process.

There are also email bounce tools that can do this for you, a few of which are listed below and will work with many of the major email marketing platforms (inclusion in Biscred's list isn't an endorsement; do your due diligence before selecting any marketing tools, including reading user reviews).

Email bounce rate tools:

Many of the major email providers (Constant Contact, ActiveCampaign, Klaviyo, HubSpot, etc.) offer built-in email address authentication in addition to accommodating bounce-rate tools.

Ask your email marketing platform's account rep:

How can they help lower your bounce rates?
How does their platform validate email addresses before emails are sent?
Does the tool perform syntax checks, verify domains and perform mailbox ping tests?

Biscred users can feel confident in the email address information that is included in our B2B CRE prospecting platform. We are continuously verifying and validating the contact information that's included in our database of over 584,000 companies, 6 million people and 3.9 million commercial buildings.

Quick Answers to FAQs on Email Bounces

Why does an email bounce?

Marketing emails bounce when they can’t be delivered—usually due to invalid addresses (hard bounce) or temporary issues like full inboxes or server errors (soft bounce).

What's the difference between hard bounce and soft bounce in email lingo?

Hard bounces are permanent while soft bounces are usually temporary. Hard bounces usually represent bad email addresses and server-side blocks. Soft bounces happen when someone's inbox is full or a message or attachment exceeds size limits.

What does it mean to be blacklisted by an email server?

Being blacklisted by an email server means your domain or IP address is flagged as a source of spam or malicious content, causing your emails to be blocked or sent to spam folders. The best defense is prevention. Make sure you follow best practices to avoid being blacklisted.

How do you prevent being blacklisted?

Avoid spammy content, such as deceptive subject lines, putting FREE!!! in subject lines, or including too many links in an email. Implement SPF, DKIM and DMARC to verify your identity and improve deliverability. Your email marketing platform manager will know what those mean, and many platforms have built-in features that test email before sending.

Sources

Mailchimp, Email Marketing Benchmarks and Metrics Businesses Should Track, last updated December 2023, accessed 2024-03-24

Google Workspace Admin Help, Gmail SMTP errors and codes, accessed 2024-03-24

Photo 55485144 | Alphaspirit | Dreamstime.com