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...