Business cards have the concept of a "holder" of each business card.
The user of the account specified when scanning the business card, photographing it from a mobile phone, creating it, or having the user changed or importing it will be the holder of that business card.
When the sender in Bulk email delivery is set to "Card Holder", the holders of each business card will be set as the senders of each email.
If, supposing multiple users have the same person's business card, the user who has the business card with the most recent date received will be set as the sender.
If the date received is the same, the user with the most recent date registered will be the sender.