In order to prevent duplicate contacts, Uptics uses the 'email address' field as a unique identifier for each of the records you import into the system, so no two contact records inside of Uptics may have the same email address.
If you have a file that is missing some email addresses, or you are using Uptics solely for Outbound Calling/SMS and Task Management, there may be a time in which you will need to import a file with no (or only some) email addresses present.
Even though the email address is used as the unique identifier for each record, records containing no email addresses will still be imported into your account.
The one caveat with importing records containing no email address, since it is used as a unique identifier, is that it will not update if you re-import additional data regarding that prospect (either via Import or via Zapier). It would, in this case, actually create a duplicate record with all of the properties from the most recent upload into Uptics.