Paperless Post stores your previously-used lists in the Address Book, so that you can use it again in the future.
On your Add Guests/Recipients page, you can access your past lists by clicking on the "Address Book" link that appears below the name/email field. You'll see "All Contacts" in the top right corner of the Address Book overlay, click that and instead select the past mailing list you'd like to use again by clicking on its name. Here's a screenshot for clarity: http://bit.ly/2njnnWh
To add these contacts as recipients for your new card, you can either click “Add All Contacts" plus sign at the very top of the list (screenshot: http://bit.ly/2mB7mwx), or you can click the + Add button next to certain contacts if you don't want to include everyone from the previous list.
Once these contacts have been added to your Unsent Guest/ Recipient list, you can add and delete to modify your list before you send.After you send your card, this list will become a part of your "Past Mailing Lists" section as well.
At this time, you cannot modify or delete past lists.