Note that in the "Patient's existing email addresses" field, if there is more than one email address, you can indicate which is the primary (default) address, by clicking in the checkbox next to it, so that it is ticked. This is the address that will be used by default for email such as automatic appointment reminders. You can still send email to other addresses (such as the patient's business email), but this must be done by selecting the address when you create the message.
Emails such as recalls, appointment reminders, appointment confirmations will be sent to all addresses that are ticked in the patient file.