Paper or email? That's the new question you may be asked the next time you buy something at a store. Customers are now being given the option to have a receipt emailed to them. But if you opt for an e- receipt, what else could start popping up in your email?

Paperless receipts are the wave of the future: major banks email customers ATM slips, mobile vendors send you e-receipts to your inbox, and the number of retail stores offering customers electronic invoices is exploding. "More customers are opting to receive their receipts via email because it's saving on paper and it's also more convenient for them," said jeweler Shaleighne Murphy. That's why Stephen Macary, a certified public accountant, loves e-receipts. He manages a fleet of company cars. When one needs an oil change, the repair shop emails him the invoice.