When you send an email, the first thing your recipient sees is the subject line, so make sure it’s as clear as possible: What is your email’s purpose? What do you want your recipient to do? Take a page from military personnel. Their subject lines use keywords in all caps to note the email’s purpose. For example: INFO – For informational purposes only REQUEST – Seeks permission or approval by the recipient ACTION – The recipient must take some action These demarcations might seem obvious or needlessly exclamatory, but they make your emails stand out in the recipient’s inbox. So if you need to send your direct reports a status update, try using the subject line: INFO – Status Update. If you need your manager to approve your vacation request, you could write REQUEST – Vacation. Using these key words also forces you to think about what you really want from someone before you contribute to their email clutter.
— Les på hbr.org/2016/11/how-to-write-email-with-military-precision