Bounces are emails that are returned to the sender without being delivered to the recipient. There are two types of email bounces: soft and hard. 

Soft bounces — Caused by temporary issues like network problems, full mailboxes or temporary server downtime. 

Hard bounces — Caused by permanent issues like an invalid/incorrect email address, a non-existent domain, or a deactivated account. 

To handle transactional email bounces in ZeptoMail, you can add the address/domain causing the bounce to the suppression list. This will prevent further email-sending to the recipient, even if they are included in your mailing list.