Email communication has its own set of etiquette guidelines for users to follow if they want to be effective communicators. which of these is not one of these guidelines?

You should definitely not type your whole email in all capitals!

Also, you should keep you message brief, this is true: people receive a lot of emails and prefer to read them fast.

I think that the first option is correct (a): Emails don't usually have headings in the text: this would make them too long.