...
The bounces section is found under Recipients > Channels > Email > Bounces
There are many types of bounces. Generally, bounces are divided in two categories: hard bounce (errors that start with 5**) and soft bounces (errors that start with 4**).
...
If you wish to, you can unsubscribe soft bounces manually, faster than what MailUp does automatically (this is typically not required). To do so, under Recipients > Channels > Email > Bounces, use the Recipient management feature (at the bottom of the page - view screenshot) and move them to Unsubscribed.