How to prevent sending any emails outside the server?

EdvardYoch

Hello everyone! I want to use mailcow dockerized like test email server, so I need to prevent sending any emails outside the server because test environment can contain real customer email addresses. But I did not find how I can do it by googling. Do you have any ideas how I can do it?

dia_moos

perhaps you can use your firewall?

like “iptables” and blocking port 25?

EdvardYoch

By iptables -A OUTPUT? Besides port 25 should I block some other ports?