Do you have enabled logging of php errors on your site? Phoca Cart does not use any own email function, it just asks for sending the emails by Joomla! methods which are set by Joomla! Global Configuration.
So try to test it step by step - first try to send emails to customers only, then try to add emails others, etc. Try to enable logging in Phoca Cart.
![Idea :idea:](./images/smilies/icon_idea.gif)
Jan