Hard bounces (misspelled addresses, bad addresses) are marked as undeliverable immediately, added to the master suppression list and the contact is suppressed.

After Campaign recognizes a contact in a database as undeliverable, the contact remains in the database as an opted-in contact. However, the contact is added to the undeliverable database/list as set in the Undeliverable settings.

Read more about removing contacts from your database that are undeliverable.