Bounce
An email bounce occurs when a sent email cannot be delivered and is returned to the sender with a failure notification.
Bounces fall into two categories: hard bounces and soft bounces. A hard bounce is a permanent failure, typically because the email address does not exist, the domain is invalid, or the recipient’s server has blocked the sender. A soft bounce is a temporary failure caused by issues such as a full mailbox, a server that is temporarily unavailable, or a message that exceeds the recipient server’s size limit. Hard bounces should be suppressed immediately; soft bounces warrant a retry before suppression.
Every bounce carries a numeric error code that explains why the delivery failed. These codes are standardised across the email ecosystem, and your email platform translates them into actionable categories. Understanding the breakdown of your bounces (what proportion are hard vs soft, and which specific codes appear most frequently) helps you diagnose whether you have a list-quality problem, a technical sending issue, or both.
For B2B marketers, bounce management is a core practice in list hygiene. Allowing hard bounces to accumulate in your database and continuing to send to them is one of the fastest ways to damage your sender reputation and reduce inbox placement rates across your entire programme. A clean list with a low bounce rate is not just better for deliverability; it also means your performance metrics are built on accurate, actionable data.
What is the difference between a hard bounce and a soft bounce?
A hard bounce indicates a permanent delivery failure. The most common cause is an email address that does not exist or has been deactivated. Hard-bounced addresses should be suppressed from all future sends immediately. A soft bounce indicates a temporary failure: the address exists, and the server accepts mail, but the specific delivery attempt failed due to a full mailbox, a server timeout, or a message size issue. Soft bounces can be retried, but contacts that repeatedly soft-bounce over time should eventually be suppressed.
How does a high bounce rate affect email deliverability?
A high hard bounce rate signals to inbox providers and blacklist operators that you are sending to unverified, purchased, or poorly maintained lists. It is one of the fastest ways to damage your sender reputation and end up on a blacklist. Most email service providers have thresholds above which they will pause your sends or require account review. Keeping your hard bounce rate below 2% is a commonly cited guideline, though lower is better.
What should I do with email addresses that bounce?
Hard-bounced addresses should be suppressed immediately and permanently; do not attempt to resend to them. Remove them from all active lists and exclude them from future imports. Soft-bounced addresses can be retried on subsequent sends, but if an address soft-bounces consistently across three to five attempts over a period of weeks, treat it as a hard bounce and suppress it. Maintaining a clean suppression list that feeds into every future send is a fundamental list hygiene practice.