Currently the Import tool matches to Contacts using an emaill address only.
As more than one contact records may have the same email address, there needs to be an option for the user performing the import to specify one or more additional fields (custom or OOB) to include in the matching process.
This feature can be particularly helpful in multibrand environments where the same email address may be found for two different brands and posted preferences need to be imported only for one of the two brands or each brand has different posted preference values. For example, the same email address subscribing to newsletter A but not newsletter B.
During the import process, the correct contact record should be identified and connected to the newly created posted preference. Currently CD wrongly connects only to the first contact matching the email address.