E-bill or E-receipt required for POS Bill

Considering going green initiative across the world, many of our customers demand e-bill for the cash memo to avoid paper based bill printing. It may be termed as e-memo, e-bill, e-receipt.

It should work like either of these options:

On saving of POS bill, a mail should be sent to the customer in his e-mail having the bill attached as PDF.
On day settlement, all the bills generated for the day should be sent in respective e-mails of the customer with bill attached as PDF (if this is the case, this can be done from HO as well).