We don't recommend deleting bad email addresses, as it is important to keep track of them. 

Click here for more information on the ways an email address is marked bad, unemailable, or bouncing in the system: nationbuilder.com/when_is_a_person_considered_emailable

If you have not already sent an email blast to these people, but know that their email addresses are bad, you can batch update them to mark them un-emailable. Learn more about batch updates here.