Gmail annotations was a big development that Google brought to promotional emails in the Promotions tab. Originally, only two annotated emails were displayed at the top of the Promotions tab.
However, it is looking like Gmail is starting to display emails with
Designing Creative Transactional Emails to Stand Out in the Inbox
Businesses that use email marketing use it explicitly to promote deals and product launches. However, they often ignore transactional emails which should be a fundamental part of their email marketing strategy. These are emails that are often overlooked as boring or unimportant,