Send admin an email when a user updates their email address in their WordPress profile.

send-admin-email-update-user.php

<?php
/**
 * Send admin an email when a user's email is updated via their Edit Profile page.
 * Full Guide - https://yoohooplugins.com/send-email-to-admins-on-wordpress-profile-update/
 * Add this code to your site by following - https://yoohooplugins.com/customize-wordpress/
 */
function yh_send_admin_email_user_updated( $user_id, $old_data, $new_data ) {

    // Send an email to an admin when the user's email changes.
    if ( $old_data->data->user_email !== $new_data['user_email'] ) {
        $to = '[email protected]';
        $headers = array( 'Content-Type: text/html; charset=UTF-8' );
        $subject = 'A user changed their email';
        $body = 'A user has changed their email from ' . sanitize_email( $old_data->data->user_email ) . ' to ' . sanitize_email( $new_data['user_email'] );
        
        wp_mail( $to, $subject, $body, $headers );
    }
}
add_action( 'profile_update', 'yh_send_admin_email_user_updated', 10, 3 );

Read the full guide here - https://yoohooplugins.com/send-email-to-admins-on-wordpress-profile-update/