One-third of all work emails that require attention go unread. Only 5% of readers make it to the end of an email, so all the things you think people are learning; they're not. The average reader spends 12 seconds on each email. 

Headlines and subject lines aren't wasted space.

The first sentence should always be what is new information from the last time you wrote.

The second sentence should explain why the topic matters to the reader. 

To keep the reader engaged, use bulleted lists and bolds. 

Emails should be short, not shallow. 

Reference: Axios, Smart Brevity