I think people should pay more attention to the subject line used in emails. When someone gets a lot of email the sender is, of course, important but so is the subject line in determining which emails should take priority.
It’s helpful when they are descriptive and give the receiver an indication of what the message is about or what it may contain.
And, it’s amazing at the number of emails that have useless subject lines or even ones that make me want to never open and read it.