Any contacts that you have sent an email Campayn to that have to and they ended up bounced, unsubscribed or marked your email as spam will be marked in Campayn and you won’t be able to send to them anymore.
Marked contacts are not be sent to again.counted towards your contact limit and even though they will remain in your lists, they will be unable to receive your Emails.
The contacts will be flagged like this:
...
We advise that you do not delete these contacts from your list so that they are properly marked and avoid the contact from being added again. Even though the contact that has either bounced, unsubscribed or marked your email as spam remains on your list and you do send to that list again, we will not count it as an email send.