Explanation
To avoid storing email addresses or phone numbers within Marketing Cloud, NTO should use Tokenized Sending2. Tokenized Sending is a feature that allows NTO to send emails or SMS messages using encrypted tokens instead of actual email addresses or phone numbers. The tokens are generated by an external system and stored in a secure database outside of Marketing Cloud. When NTO sends an email or SMS message, Marketing Cloud sends the token to the external system, which decrypts it and returns the actual email address or phone number. This way, NTO can avoid storing sensitive information in Marketing Cloud. The other options are incorrect because:
Field Level Encryption. This is a feature that encrypts specific fields in data extensions using encryption keys managed by NTO. However, this feature does not prevent NTO from storing email addresses or phone numbers in Marketing Cloud; it only encrypts them within data extensions.
Lookup reference to Contact Object. This is a method that allows NTO to use a lookup field in a data extension to reference a contact attribute from the Contact Object in Contact Builder. However, this method does not prevent NTO from storing email addresses or phone numbers in Marketing Cloud; it only reduces the duplication of data across data extensions.
Master-detail relationship to Contacts. This is a type of relationship that allows NTO to link a data extension to the Contacts data model in Contact Builder. However, this type of relationship does not prevent NTO from storing email addresses or phone numbers in Marketing Cloud; it only enables them to use contact attributes for personalization and segmentation.