So each e-mail is worth about 100 breaths.

The Economic Times reports:

Breath calculation is as follows:

Average person exhales about 0.9 kg (31.68 oz.) CO2/day.

Adults exhale about 30,000 times/day.

31.68 oz. divided by 30,000 breaths = .0011 oz. per breath. So 100 breaths produces about 0.11 oz. CO2.