What constitutes a temporary delivery issue categorized as a soft bounce?

A soft bounce refers to a temporary delivery issue that prevents an email from reaching the recipient's inbox. When the inbox is full at the moment of sending, the email server cannot accept new messages until some space is available. This situation is temporary, allowing for the possibility that the email may be successfully delivered at a later time when space is cleared in the recipient's inbox.

Other scenarios, such as an email address being constantly invalid or a permanent change in an email address, indicate persistent issues that are not soft bounces, as they require different handling and usually result in a hard bounce. Similarly, if an email is flagged as spam, it may not even reach the inbox; however, this is not classified as a bounce type but rather as a filtering issue. Thus, the definition and characteristics of a soft bounce align perfectly with a full inbox scenario.