Dropped email addresses have bounced back enough times that messages are no longer sent to them
Go to Analytics from the Menu Bar and click on your Message.
Click on Email above the Rates Tiles right then on the Drop Rate tile to open a list of Dropped email addresses.
Click Export for a spreadsheet of Dropped email addresses. Once these email addresses have been updated in your AMS they will automatically appear in NoteRouter. If a contact confirms that a dropped email address is correct (like in the case of a new member who was sent an email before their email inbox was fully set up yet,) you can Reenable Deliveries to them from their profile under Manage > Contacts.
Note: NoteRouter stops sending messages to Dropped email addresses in order to protect your Reputation with email providers.