A lot of those emails asking you to send it to x number of people in x amount of time, and if you break the chain you will have bad luck are Phishing (fishing) scams looking for email addresses that can be sold to other scammers. They open you, and all of your friends, to getting all that junk, porno, and "specialty item" sales emails.
By sending them thru, you are verifying a live address, plus you are giving them x number more. If you do choose to send them on, be sure you delete the promise/threat at the bottom, as that is usually where the code is hidden for the collection of email addresses.
Also, NEVER forward emails with others addresses on it, always copy and paste the text you want into a new email to send. That stops the chain.
This information was given to us by a very competent tech guy at the last place I worked. He knew all about what he was telling us, as he was a former hacker himself.