Is he getting ALL email notifications of new topics in your community? Or just email notifications of topics he had participated in or was otherwise following? The latter is a mechanism of general Get Satisfaction user accounts and has nothing to do with being an employee. The former only occurs for people listed as an Employee in a community here. If he wants to stop receiving all email notifications, he needs to access his own user profile and uncheck that box, like so:
If he's still receiving email notifications of all new topics in your community then we'll have to investigate. If that's the case, please email our support email address with his name and email address so we can look into it. Thanks!