Now, look at the sentence you have written.

• Is this what you would say to the primary readers, face-to-face?
• Would it make sense to them, on its own?
• Is it appropriate?
• Would they be interested?

Your message should be the kind of sentence that would grab the readers' attention and force them to keep listening. It should also summarise everything else you want to say. (It's best, therefore, for the message not to be a question, or for it to consist of question and answer.)