You've learned how to send an email when a user changes their password using SendGrid's Mail Send endpoint and Auth0 Actions. You set up your SendGrid account, created an API key, and wrote an Auth0 Action that uses the SendGrid Mail Send endpoint to send a password change email to users. The Action was tested and deployed, then added to the Post Change Password flow in Auth0, allowing it to trigger automatically when a user changes their password. This feature enhances security by keeping users informed of changes to their account information.