Bounces are handled automatically by the software. If an email address is a hard bounce (meaning the email address does not exist), then they are bounced from your list right away. For soft bounces (i.e. mailbox over quota, temporarily disabled, etc...) it takes 3 soft bounces before an address is removed from the list. Bounced emails are set to a status of "Bounced" so you cannot re-add them accidentally.