E-mail marketing is valid and powerful as King pin says. Tesco I believe are the biggest users of e-mail marketing in the UK and send out millions every day - can't remember the exact figure but it is scary.
If the mail has a relevant offer and is personalised it will often get opened. I just got one from Tesco this week saying that I hadn't shopped online for a while here is a £10 voucher.
The concepts will be similar this might help although obviously different.
http://www.royalmail.com/portal/rm/c...diaId=37200672