It is not possible to suppress e-mail messages from a test environment, but what you can do is:
- Go to Application Management > System Settings: General, change the installation mode to a value other than "production" and change the setting "Recipient of all outgoing e-mails" to an address where you want to receive these e-mails. All e-mails will then go to this address.
- Add a rule to your e-mail application itself that allows you to move all e-mails from the test environment to a separate folder immediately upon receipt.