According to Club Green IT, sending 33 e-mails of 1 MB to two recipients per day would produce 180 kg of CO2 per year, the equivalent of 1,000 km travelled by car.

According to the organization Carbon Literacy Project, 4 grams of CO2 are generated by sending a standard email, and up to 50 grams with a large attachment. Sending a 1 MB vacation photo to 10 friends would be equivalent to driving 500 meters. 

These figures make us think twice about clicking on the "attach files" button. But what are our alternatives?