A contact list can have zero contacts, but there is no limit to the number of contacts on a list.

You might use an empty contact list in the following ways:

• To create a list by uploading a file of contacts that you already own. The file used in the upload is limited to 5mb. 
• To create a list by pulling in contacts based on dynamic rules.
• To create a list by manually pulling in contacts that already exist in the account.

When uploading a contact list, you will be asked to confirm that all contacts have opted in to receive email marketing from you, or to sen an opt-in email to all of your contacts. Review What is the Anti-Spam law? prior to uploading contacts to ensure that you are following the laws that apply to the country or region you are sending emails to or from.