Contacts is the new way to organize your subscribers in Mailpro, it will allow you to have more organized your subscriber lists while providing better data when it comes to viewing your statistics. In contacts each Email is unique no matter how many lists it is in, it will not have repeated emails and it will be very easy to include a subscriber in another list without having to create it again. We also added the Tag options, which are nothing more than a way to categorize certain contacts, either by activity or by where they have been subscribed.
The best reason why you should migrate your address books are the Segments, with them you can make a more specific filter when sending messages. You can segment by some field, activity or label, you can also combine these conditions and thus send a message to your target audience. If you want to know how to migrate your address books, we invite you to see How to migrate my Address Books to Contacts.