From the book How Bad Are Bananas?, published in 2010 by the researcher Mike Berners-Lee, which gave 4 g for an ordinary email and 50 g with long attachments. The 2020 edition of the same book gives 0.2 to 0.3 g for a short email and 17 g for a long one, according to the Carbon Literacy Project. ADEME's Base Carbone contains a 4 g value for "1 email", created in 2014 and still online in October 2026.
Read the source article: Carbon footprint of an email: about 2.5 gCO2e for 1 MB