How to allow users to send Approved email templates for person Accounts but not to business Accounts in CRM?
The Send Email button is driven by permissions to the Sent Email object (for iPad and Windows app) and page layout driven for Online. The user cannot restrict the Send Email button from appearing on the Business Accounts. This has to be an enhancement.
Do not give the users access to the email field on the Business Account. Another option is to exclude the email field on Business Accounts from appearing in Approved Email UI, so reps are not able to send emails. See the online help documentation on how to exclude fields from appearing in Approved Email.
CRM Help Documentation: Components of Approved Email