Hard bounce means that email delivery to a certain recipient fails on a permanent basis. Most of the time, recipients themselves cause hard bounces to happen.

Hard bounce reasons

  • invalid email addresses;
  • invalid domain names; or
  • the email server of the recipient, by policy, blocks the delivery.

It happens sometimes that subscribers, for personal reasons, do not wish to give out their real email address. So when filling in the form on your website or landing page, they insert a random email address just to pass the procedure requirements. 

However, it may occur that valid email addresses are giving hard bounces, or the subscriber could have unsubscribed by mistake, and this caused a hard bounce. In such cases, the subscriber needs to opt-in once again to be in your subscribers’ list.

In case of a hard bounce, the sender gets an auto responder email, also called a delivery notification.


  1. SendGrid states the difference between hard bounce and soft bounce and offers tips to avoid them.
  2. HubSpot identifies and compares hard bounce and soft bounce.
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