"One of the main factors that determines the carbon footprint of an email is its size. The larger the email, the more data it transfers, and the more energy it consumes. For example, a simple text email of 1 KB (kilobyte) can emit about 0.3 grams of CO2, while a rich email with images, attachments, and HTML of 1 MB (megabyte) can emit about 300 grams of CO2. That's a thousand times more! Reducing the size of your email can significantly lower its environmental impact."
https://www.linkedin.com/advice/0/how-do-you-make-your-email-design-carbon-efficient
@gerrymcgovern We think of email as carbon neutral! Of course it uses... electricity!