How can you store your Bolletta Web?
Whether or not you're obligated to print a bill you've received electronically (via email) varies depending on the type of customer.

Are you a residential customer?
You can save the bills on your PC and print them only when necessary.

Are you a business owner or do you have a VAT number?
The current Italian civil and tax law requires businesses and professionals to print electronically received documents* related to their business activities.  

* If you receive Bolletta 2.0, you only need to print the summary bill to satisfy tax requirements.