Getting Hard Bounce Responses for email addresses included in a campaign will prevent you from sending emails to those email addresses for a certain period of time

Based on Answer Id: 9394 Bounced Email:

If you have set up DKIM and an email domain, you can send email to the email address after 30 days. If you have not set up DKIM or an email domain, you can send to it after 90 days have passed. If you send to a bounced email address before the time has elapsed, the email is not sent, and the campaign response is reported as Failed - invalid address.

Note:

It is important to understand that this only applies to hard bounces. The actual behavior of the product is that, if a message is rejected with a persistent failure -- user unknown/mailbox doesn't exist -- then subsequent delivery attempts will be suppressed.

A message being blocked for spam, server errors or anything aside from a positive confirmation from the recipient that the address will never be deliverable will not result in future delivery attempts being suppressed.