What steps does an administrator need to take to enforce TLS with a particular domain?

Secure Transport Compliance:

TLS (Transport Layer Security) ensures that emails are encrypted during transit between sending and

receiving email servers.

Setting up secure transport compliance ensures that emails sent to or received from a particular

domain use TLS.

Steps to Enforce TLS:

Navigate to the Google Admin console.

Go to Apps > Google Workspace > Gmail > Advanced settings.

In the "Compliance" section, select "Secure transport (TLS) compliance".

Click "Add setting" and configure the following:

Select the appropriate organizational unit.

Specify the receiving domain(s) for which TLS should be enforced.

Choose to enforce TLS for incoming, outgoing, or both types of messages.

Save the changes and apply them.

Reference

Google Workspace Admin Help: Set Up TLS Compliance