It's really quite simple! Here's a great example of an e-mail that I'd never reply to:
i got book thru men's health wondering do you increase weight use when reps increase by 20% or overall weight lifted. weight x total reps im 40 5ft 6 180 lbs would like to lose 25-30 lbs without loosing much muscle or gainning some. second email sent. ps i have not paid for book i can still send back ant help would be appreciated would like to try program for the three weeks allowed to decide if i think it works. i have been working out for 27 yrs so i need alot of variety in workout.
First, the complete lack of punctuation, spelling, and sentence structure make it impossible to discern what this individual is asking.
Second, this individual expects me to answer his questions about my book, which he hasn't even purchased! I'd also wager that he hasn't read it, because if he had, his questions would be answered.
He also wants me to write him a program gratis, but that's a subject for another day.
Free advice is worth what you pay for it. Bad e-mails on the other hand, are a complete waste of time, both for the sender, and for the recipient.
OK, I feel better now, thanks for humoring me...