Blackbaud applications will automatically exclude hard bounces email addresses and invalid accounts from your bulk email or email blast. Hard bounce email addresses are stored in Invalid Accounts in your Blackbaud application. These do not have to be removed from the list manually.

For the most up-to-date information regarding how the system excludes addresses from Processing, consult our Email Delivery FAQs: 
https://bb-email-services.docs.blackbaud.com/faqs/processing/#ProcessingExclude

For more information:
How long does Blackbaud NetCommunity attempt to deliver emails they are considered bounced? 
What is a hard undeliverable email (hard bounce)