A page’s download time client-side directly correlates to the number and size of files the browser has to download.

For each file, the browser sends a GET HTTP to the server. It waits for the response, and then downloads the resource as soon as it is available. Depending on the type of web server you use, the more requests per page there are, the fewer pages the server can handle. Reducing the number of requests per page is key to reducing the number of HTTP severs needed to run the website, and consequently its environmental impact.

There are several ways to reduce the number of requests per page: - Combine static files e.g. CSS and JavaScript libraries (see best practice #81) - Use a CSS sprite (see best practice #23) to group the interface’s images - Favor glyphs over images (see best practice #18) and, in general, vectors over bitmaps. - Fill the browser cache as much as possible.

According to Ademe (Environment and Energy Management Agency), an email containing a 1 MB attachment has a carbon footprint equivalent to 19 g of GHG emissions. If we apply this figure to a company with 100 employees, sending an average of 332 emails each day, 220 days per year, this amounts to 13.6 tons of GHG emissions, the equivalent of 13 return flights from Paris to New York.
Some other figures: according to Google, for a French company with 500 employees and its own email servers, each user will consume approximately 16 kWh and the equivalent of 1.67 kg of GHG emissions sending and receiving emails every year.
With these figures in mind, it is essential to systematically check that no users are subscribed more than once before sending a mass mail or newsletter.