The correct answer is: sometimes.
Advertising sometimes changes the usage of a word. It provides a different meaning or connotation to a word to get the audience attention. In other words, they have to convince people to buy what they are selling, their product.
Moreover, changing the usage of a word in the advertising world is only a tool. It isn't something that always happens, or that hardly ever happens.
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.
