I got the mail as well, it is an official mailing
2 years ago I competed in a contest on the ACO site (lemans.org) and had to fill in my email and address.
Every now and then since that time I recieve an email with offerings and even the odd letter in the mail trying to inlist me into their membership
Very rare though so not bothering me
edit: when you go to the aco site not using the link you will find the same offer, so definately trustworthy