How to Clean up Subscriber Email Addresses in the Email Marketing Module

Here are the steps to clean up the email addresses.
 
To remove the invalid email addresses
Marketing > Broadcast Email
Subscribers tab > Emails tab:

 
Select the All Items report view.
Select "invalid" from the Status menu:

 
You can delete these by batch-selecting them, and then choosing Delete from the Action menu.

 
Managing Pending email is done the same way, but with "pending" selected from the Status menu:

 
The Duplicate number does not necessarily reflect duplicate email addresses in the database.  The number indicates the quantity if email addresses in that campaign.  If you have an email address in multiple lists and you include more than one of those lists in the campaign then that email address will be considered to be duplicated for that campaign.
 
The same is true for the Opted Out count.  These can also be managed via the Subscribers tab.
Subscribers tab > Excludelist tab:
Select "opt-out" from the REASON ADDED menu: