When an email isn't delivered to a contact, it's either because of a hard or soft bounce.
A soft bounce indicates that the email address is valid and has reached the recipient's mail server, but for some reason, the email wasn't delivered to their inbox. There are a number of reasons why this could happen. Some reasons include that their inbox was full or the server was down.
Because soft bounces are temporary, we don't prevent that contact from receiving emails in the future.
A hard bounce indicates that an email address is permanently invalid. Meaning, the URL or the email address doesn't exist.
As soon as a hard bounce occurs, that contact will be blacklisted and will no longer be sent messages from Kizen.
You can then create a group of your blacklisted email accounts in order to clean your list periodically.