This happens when we use different typology rule in the delivery activity. If we define these rules in typology, mail gets triggered-Subject validation, URL label validation, Approval of URLs, Message size validation, Unsubscription link validation, Check proof target size, Check delivery size, Wave scheduling check, Social network sharing link validation, Deco-mail check. When we use these rules, mail does not get triggered in stage environment-Subject validation, URL label validation, Approval of URLs, Unsubscription link validation, Wave scheduling check, Deco-mail check. It is working fine in lower environment.