If you already have an existing database of contact information, you could import the same onto your Freshdesk Account, from under Customers-->Import. You would have to upload a .csv file containing the contact information and map the columns to contact fields on your account.

Once this is done, the contact information would be uploaded into your Freshdesk Account and would be accessible from under the Customers Tab. The Activation Email would not be automatically sent to the contacts from your Freshdesk, while being imported.