What is Hard Bounce and Soft Bounce In Salesforce Marketing Cloud?

Soft Bounce
A soft bounce occurs when the email server rejects the email message due to a seemingly temporary condition, such as:

Address is temporarily unavailable due to an inactive or temporarily disabled mailbox
Recipient's mailbox is full
Temporary domain failure
The Marketing Cloud will make 288 attempts to deliver the email message. If all attempts are unsuccessful, it is considered a soft bounce.

Types of soft bounces include:

• Block Bounce: Occurs when the email server rejects the email message due to filter issues, such as:
  Complaints
  Blacklisted IP address
  Content-related issues
  URLs within the email message are blocked
  Improper authentication
• Technical Bounce: Occurs when the email server rejects the email message due to technical errors, such as:
  The server is too busy/temporarily overwhelmed
  Formatting or line length errors
  Network connection lost or timed out

Hard Bounce
A hard bounce is an email message that is undeliverable for permanent reasons, such as:

Bad/nonexistent domain
Invalid or fake email address
High number of unknown/inactive addresses on a list