Definition - What does Soft Bounce mean?
A soft bounce refers to any email message that is returned or bounces back due to any temporary availability issue with a recipient's mailbox or mail/domain server. It is a type of bounced email message that is visible or received only when the recipient is incapable of receiving the message.
Techopedia explains Soft Bounce
A soft bounce is primarily a delivery error email message that is automatically sent to an email sender.
A soft bounce occurs in the following situations:
The recipient’s mailbox is full and cannot receive more messages. The recipient must empty or make enough space in the mailbox.
The recipients email server is offline or currently unreachable. The sender, in this case, must wait.
The size of the email message is larger than base limits of the host's or recipient's email server/host/domain.
If an outgoing email encounters any of the above situations, the sender receives an auto-generated soft bounce message specifying the reasons why the message cannot be delivered at that time.