Use any of the below two ways.
var id = ""; // sys_id of the group
var gr = new GlideRecord('sys_user_group');
gr.addQuery('sys_id',id);
gr.query();
if(gr.next()) {
gs.info('Group Object - '+gr);
}
-------
var id = ""; //sys_id of the group
var gr =...
You can also change the email label/from field of the service account via sys_email_account table for type as SMTP for all the emails send from your instance.
If it is in scoped app then it should be called via scoped app name to the REST Message.
Also check if your post http method is defined in the related rest message.
