Hard bounce

There are two types of email bounces: hard bounces and soft bounces. While soft bounces are temporary delivery outages that often resolve over time, hard bounces are permanent delivery failures to recipients’ inboxes.

A hard bounce occurs because of an invalid email address, inactive receiving server, or because the message is flagged as spam content, all of which result in inbox service providers (ISPs) rejecting the email. Hard bounces indicate bad deliverability and impact future deliverability. ISPs are less likely to place a brand’s emails in its subscribers’ inboxes in the future if they have a history of hard bounces.