If you would like to send mass emails to your customers, you have 3 options:
Assigned contact/private individual: If a Default contact person is assigned to a card, the email will be sent to their default email address. If there is no default contact person, the email will be sent to the email address added to the business.
Business: The email will be sent to the default email address of the card.
All contact persons: The email will be sent to all contact persons by default. If you filter to personal data, for example, position, only those will receive the email to whom the filter condition refers.