Why are test emails sent to the Account email address rather than the Approved Email Test Email Address listed in the Approved Email Settings Custom Setting?
If the Approved Email Test Email Address field in the Approved Email Settings Custom Setting is left blank, test emails sent from Sandbox environments are sent to the address listed on the account.
Entering an email address in this field causes all emails sent from Sandbox to be sent to this address by default. This helps prevent accidentally sending emails to unwanted recipients. It is good practice for testers to look for the warning message displayed in the Send Email screen indicating that the email will be sent to the test address.
CRM Help Documentation: