If you are unlucky enough to receive an email suggesting M&S will pay you in vouchers for forwarding the email (£100 for 8 forwards and £500 for 20) DO NOT FORWARD as this is a SCAM.
The email claims that Persimmon Homes is in a deal with M&S for word of mouth marketing. You are required to cc your forwarding email to someone at Persimmon Homes, but the email address is not a valid one for Persimmon Homes.
I received one yesterday and oh you lucky friends out there, I looked into it first. It didn't make any commercial sense to me, then I noticed the email address was invalid, then I did some net research and this is not the first time this has happened. I now expect spam. Lots.