DLP e-mail External Domains

Hello,

I'm working on creating a Data Loss Prevention (DLP) policy that analyzes the domains of email addresses in the TO, CC, and BCC fields. The goal is to implement the following functionality:

1. Check for different external domains across these fields.
2. If multiple external domains are detected, display a warning message to the sender.
3. The warning should appear as a tip or pop-up, stating: "Email addresses from different external domains have been detected."
4. The email should only be sent after the user confirms their intention to proceed.

This policy aims to prevent accidental data leakage by alerting users when they're about to send an email to multiple external organizations simultaneously. It adds an extra layer of security by requiring user confirmation before sending such emails.

Could you please advise on the best way to implement this DLP policy using Microsoft Purview (formerly Microsoft 365 Compliance Center)? I'm particularly interested in:

1. How to create the custom condition to check for multiple external domains.
2. How to set up the warning message as a pop-up or tip.
3. How to implement the user confirmation step before allowing the email to be sent.

Any guidance or sample configurations would be greatly appreciated. Thank you for your assistance!