Unraveling the Mysteries of Email Bounces: Hard Bounce vs. Soft Bounce

Aug 18, 2023 | Blog, Deliverability

We’ve all experienced that sinking feeling when an email we carefully crafted fails to reach its intended recipient. Despite meticulous configurations, email bounces can still occur due to a myriad of reasons, some within our control and others beyond it. In this article, we’ll dissect the realm of email bounces and delve into the crucial distinctions between two pivotal categories: hard bounces and soft bounces.

Understanding these distinctions is paramount for honing your email marketing campaigns and maintaining your sender reputation.

The Duel: Hard Bounce vs. Soft Bounce

As you navigate the labyrinth of email bounces, you’ll often be greeted by an automated response notifying you of an error. These notifications provide insights into the underlying causes, helping you decipher the error’s nature and its potential solutions.

The world of email bounces can be complex, but categorically, they fall into two major types: hard bounces and soft bounces.

Hard Bounce: The Unreachable Territory

A hard bounce signifies a permanent failure in delivering an email. Once a hard bounce occurs, any subsequent attempts will also fail.

This type of bounce commonly stems from typographical errors in email addresses or rejections by the recipient’s Internet Service Provider (ISP).

Invalid Email Addresses: A simple typo or an inexistent domain can trigger a hard bounce, severing the email’s path to the recipient.

ISP Rejections: Sometimes, email servers deem your communication unworthy for various reasons, resulting in a hard bounce.

Soft Bounce: The Resilient Hurdle

Unlike its rigid counterpart, a soft bounce signifies a temporary setback in email delivery. The email server will often make subsequent attempts, allowing room for resolution. Patience can be your ally when dealing with soft bounces.

Mailbox Full: A common cause of a soft bounce, an overflowing mailbox, can be remedied by the recipient clearing their inbox.

Message Size Limitations: Emails that exceed size limits might initially bounce softly, with servers attempting retries before deciding on a hard bounce.

Unveiling the Causes: A Deeper Dive

Causes of Hard Bounces:


  1. Nonexistent Recipient: A mistyped address or obsolete email domain can result in a hard bounce.
  2. Server Blockage: Spam filters can unfairly reject legitimate emails. Implementing proper authentication, such as SPF, DKIM, and DMARC, can mitigate this.
  3. Reputation-Based Rejection: Consistently unopened emails may lead to servers preemptively rejecting future messages. Regularly cleaning your email lists is advisable.
  4. Mailbox Full and Abandonment: A full mailbox might temporarily bounce emails, but repeated bounces may indicate an abandoned account.
  5. Challenge-Response Errors: Some systems require sender authentication through challenges. Ignoring these can lead to a hard bounce.
Causes of Soft Bounces:


1. DNS Failure: A hiccup in the Domain Name System can cause temporary soft bounces.

2. Message Size Exceedance: Messages surpassing size limits might softly bounce before potential retries.

3. Recipient Limits: Some ISPs restrict incoming emails to prevent spam, leading to soft bounces for legitimate messages.

4. Autoresponders: Autoresponders, especially during holidays, might temporarily bounce emails. Review autoresponders for potential updates.

The Path Forward: Navigating Bounce Management

Successfully navigating the realm of email bounces requires strategy. Employ these tips to manage both hard and soft bounces effectively:


1. Verify Recipient Addresses: Double-check email addresses to avoid hard bounces caused by typos or nonexistent domains. This can be done automatically, if you use double opt-in on your list.

2. Authenticate Sender Identity: Implement SPF, DKIM, and DMARC to enhance email deliverability and minimize hard bounces.

3. Regular List Cleanup: Keep your recipient list updated to prevent reputation-based rejections. Remove in-active recipients – this can be done automatically with a sunset-flow.

4. Engagement Tracking: Monitor recipient engagement to address potential reputation-based rejections.

5. Message Size Consideration: Be mindful of email attachment sizes to prevent soft bounces.

6. ISP Limits Awareness: Familiarize yourself with recipient ISP limits to avoid soft bounces due to message size or quantity.

7. Autoresponder Insights: Review autoresponder messages to identify potential mailbox abandonment or contact updates.

Conclusion: Navigating the Bounce Conundrum

Mastering the world of email bounces empowers you to refine your email marketing campaigns and maintain high deliverability rates. The distinction between hard and soft bounces serves as a beacon, guiding you towards effective bounce management.

Remember, conquering email bounces requires a combination of vigilance, understanding, and strategic measures. By unraveling the complexities of bounce types and their underlying causes, you pave the way for smoother email communication and more successful marketing endeavors.

Heysender blog

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