Send email using CSOM to authenticated external users in SharePoint Online

SendEmailExternalUser.cs

using Microsoft.SharePoint.Client;
using Microsoft.SharePoint.Client.Utilities;
using System;
using System.Security;

namespace ExternalUsersEmail
{
    class Program
    {
        static void Main(string[] args)
        {
            //Authenticated ClientContext. I am using SharePointOnlineCredentials but YMMV.
            var clientContext = GetClientContext();

            var web = clientContext.Web;

            //Full logon name of the authenticated external user you want to send the email to.
            web.EnsureUser("i:0#.f|membership|paige.turner_contoso.com#ext#@tenant.onmicrosoft.com");
            clientContext.ExecuteQuery();

            var emailProperties = new EmailProperties();
            //Email of authenticated external user
            emailProperties.To = new string[] { "paige.turner@contoso.com" };
            
            emailProperties.Body = "This is the email body";
            emailProperties.Subject = "This is the email subject";
            Utility.SendEmail(clientContext, emailProperties);

            clientContext.ExecuteQuery();

        }

        private static ClientContext GetClientContext()
        {
            string siteUrl = "https://tenant.sharepoint.com/sites/comms/";
            var clientContext = new ClientContext(siteUrl);
            string passwordPlainText = "userpassword";
            string currentUserLoginName = "user@tenant.onmicrosoft.com";
            var passWord = new SecureString();
            foreach (char c in passwordPlainText.ToCharArray()) passWord.AppendChar(c);
            clientContext.Credentials = new SharePointOnlineCredentials(currentUserLoginName, passWord);
            return clientContext;
        }
    }
}

Its not working in my case, I can send email from outlook but Programmatically , i can't send EMAIL. Is there any specific licence needed for send email.?