There are two types of email bounces to consider. One is a soft bounce, which means that your email hasn’t been delivered to a subscriber for a temporary reason (e.g. the recipient’s inbox is full, or their server is down). A soft email bounce means that your emails stand a chance of being delivered in the future.
A hard bounce happens when an email address is invalid. This could be because the recipient has changed their email address or that it’s been inputted incorrectly. Hard bounces mean that your emails will never reach the affected subscriber, not now, nor in the future. Hard bounces should be “cleaned” from your subscriber list immediately.