DDG email is a service which acts as a barrier between you and people you receive emails from. It removes all trackers from your emails. However, to send email from this @duck.com email address, you need to tweak the username a bit.

This tool takes in the relevant parameters and generates that email address for you. When you send the email from to the address, it goes to DDG server which send the email from DDG ID.

So your real address is not exposed.