A hard bounce in email marketing typically occurs when an email is permanently rejected by the recipient's email server due to the recipient's email address being invalid. This can happen for various reasons, such as the email account being deleted, the domain no longer existing, or a typo in the email address.
Hard bounces are a critical metric in email marketing as they directly impact deliverability rates and sender reputation. It's essential for marketing teams to monitor hard bounce rates and take proactive measures to clean their email lists regularly to maintain high deliverability and engagement rates.
References: Salesforce Marketing Cloud documentation on email deliverability provides insights into understanding and managing hard bounces, including best practices for maintaining a healthy email list and ensuring high-quality data management.