A soft bounce is an email delivery issue when you cannot deliver emails to a recipient. Soft bounces happen due to temporary issues, like a full mailbox, the recipient’s email server being down or offline, or the email message being too large.
When this happens, the sender’s email server will receive a notification that the email was not delivered.
Soft bounces are not as serious as hard bounces. You can resolve them with simple tweaks in your email settings.