Importing new contacts
Selecting the consent status is a required field on the import settings page. From the dropdown selector select the consent status of contacts about to be imported and describe how consent was collected.
If you import contacts as having provided express consent it's your responsibility to have documentation available to show where, when and how consent was collected should there be a spam complaint.
Re-importing existing contacts
When you're re-importing existing contacts you can choose to keep existing consent statuses unchanged or update consent status as contacts are re-imported.
Consent status will be unchanged for existing contact by default. If you wish to update consent status of existing records when you're re-importing lists, uncheck the "keep consent status unchanged" option on the import settings page.