A contact list can have zero contacts and is only limited by the size of the file (5mb).
All contact lists in Zift123 default as Opt-In, but the user also has the ability to send an opt-in confirmation email to the contact.
You will be asked to confirm that you have permission from the recipient to add them to your list. Is is important that you understand that Zift Solutions abides by anti-spam laws. We do not tolerate any form of spamming.