There is a limit for the number of leads you can import at once, and it is set at 2,000.
However, after selecting these initial 2,000 contacts and starting a campaign, you can repeat the search and the contacts you have already downloaded from the DataUnlimited are automatically excluded.
This means that you will never download them twice.
So, this limit prevents you from including duplicate contacts in your campaigns and makes sure that all the contacts in a single campaign are unique.
In addition, this process encourages you to create relatively smaller campaigns in terms of the numbers of recipients, so that you can test different options and change the copy more often.