Why did my email bounce?

Think of it like sending a letter through the mail and having it returned because something prevented it from reaching the address.

The reason the email was rejected determines the type of bounce.

Hard Bounce

A hard bounce indicates a permanent delivery failure. The email address cannot receive messages, and retrying will not resolve the issue.

Common reasons include:

• Invalid email address: The address may contain a typo or does not exist.

• Nonexistent domain: The domain portion of the email (after the @) is not valid.

• Authentication failure: The sending domain fails email security checks.

• Server-level block: The receiving mail server has blocked messages from your domain or IP.

Repeated hard bounces can negatively affect your sender reputation and reduce deliverability across your campaigns. When a hard bounce occurs, the address should be removed from your sending list to protect your email performance.

Soft Bounce

A soft bounce indicates a temporary delivery problem. The email address itself is still valid, but something prevented the message from being delivered at that moment.

Common reasons include:

• Inbox storage limits: The recipient’s mailbox has reached its capacity.

• Message size limitations: The email or attachments exceed the recipient server’s limits.

• Temporary mail server issues: The receiving server is unavailable or overloaded.

• Spam filtering: The email was flagged or temporarily deferred by a filter.

Soft bounces do not necessarily require removing the contact. Most email platforms automatically retry sending the message over a period of time. If the issue persists after several attempts, the address may eventually be classified as a hard bounce.

What Bounce Rates Say About Your Email List

Bounce rates are a useful indicator of list quality.

A high number of hard bounces usually suggests problems with the list itself. This can happen if:

• addresses were never validated

• the list contains outdated contacts

• contacts were added without verification

Soft bounces are more common and often resolve on their own. However, if the same address repeatedly soft bounces, it may indicate the account is inactive or filtering your messages.

Monitoring bounce patterns can help identify issues with both your list hygiene and sending practices.

Why Bounce Rates Matter

Mailbox providers like Gmail, Outlook, and Yahoo track how your emails perform. When a large percentage of messages bounce, it signals that your sender may not be maintaining a healthy mailing list.

As bounce rates increase, providers may begin to:

• filter more of your emails into spam

• reduce inbox placement

• block messages entirely

Lower visibility leads to fewer opens and clicks, which can further damage your sender reputation over time.

Most email platforms also enforce bounce rate thresholds. If those limits are exceeded, sending privileges may be restricted or temporarily suspended.

Maintaining a clean, engaged list is one of the most important steps you can take to ensure reliable email delivery. Take a look at our article on email deliverability best practices for more tips!