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Why Do Emails Bounce? Soft Bounce vs Hard Bounce

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. 


This guide to bounced email codes should help email marketers and sales teams diagnose delivery issues so you can take appropriate actions to maintain a healthy email list.


Definition of Bounced Email

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 Are Hard Bounces?

Hard bounces are emails that you likely cannot resend. Meaning, 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?

Soft email are email bounces that you likely will be able to resend. They tend to be temporary, such as when a server is down or a recipient's mailbox is 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 215,000 companies and 560,000 people. 


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

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