What is an email bounce?
When an email bounces, it does not always mean there is a serious problem, but it is helpful to understand why it happens
An email bounce occurs when a message cannot be delivered because the receiving mail server rejects it.
A hard bounce means delivery is permanently impossible. This usually happens because the address does not exist, contains a typo, includes unsupported characters, or is incomplete. Hard bounces will not resolve unless the email address is corrected.
A soft bounce is a temporary failure. The address is valid, but delivery is blocked due to issues such as a full inbox or a temporary problem with the recipient’s email provider. Once the issue is resolved, resending the email often succeeds. Some email service providers will convert repeated soft bounces into hard bounces after multiple failed attempts within a set timeframe.
What happens when emails bounce?
Bounced emails are not delivered, which means recipients may miss important messages. Over time, a high number of hard bounces can damage your sender reputation. This increases the risk of messages being routed to spam folders or blocked entirely by email service providers.
How to avoid email bounces
Clean and accurate email data is the most effective way to reduce bounces.
Use a double opt-in process so subscribers confirm their address before being added to your list. This helps catch typos and ensures the address belongs to the subscriber. For existing lists, email validation can identify invalid or risky addresses. Infobip offers an email validation service for this purpose.
How to measure email bounce rate
Email bounce rate is calculated by dividing the number of bounced emails by the total number of messages sent in a campaign. As a general benchmark, a bounce rate above 2 percent indicates that your email list quality needs attention.
Other reasons an email may bounce
Not all email bounces are caused by invalid addresses.
Emails can also be rejected due to domain-level issues, such as a misconfigured or temporarily unavailable mail server. Authentication failures related to SPF, DKIM, or DMARC policies may also cause receiving servers to block delivery.
In some cases, bounces are triggered by sender reputation rules, rate limits, or provider-specific policies. These rejections are often classified differently across email service providers and may not clearly appear as hard or soft bounces.
Occasional email bounces are expected and happen even with well-managed lists. What matters is understanding the cause and responding early. With the right controls in place, email delivery remains predictable and under control.
