The cost of
sending an email.
It feels free. But a little energy, a little hardware, and a lot
of tiny processes make every email possible. Let’s add them up.
A small action, at any scale.
ILLUSTRATIVE MODEL · GBPEnter a whole number from 1 to 1,000,000.
for 10,000 emails
Resources used to send and store. No profit margins or subscription fees.
Where does it go?
The raw ingredientsA model, not a bill. Actual costs depend on the devices, network, and provider involved. See every assumption
More emails.
Less per email.
Opening a connection takes resources. Do it once for a whole batch, and that small setup cost gets shared.
Quantity uses a logarithmic scale. The curve flattens: every extra email still uses resources.
Nothing hidden.
Just the maths.
Every number above comes from the assumptions below. Change them to explore a different setup.
EDITABLE ASSUMPTIONS01 The assumptions
Illustrative engineering inputs, not measurements of a particular email service. All prices are in GBP.
Sender: 25 W device; 10 seconds of setup + 0.2 seconds per email. £800 hardware over 4 years × 2,000 active hours/year.
Delivery: 20 W of allocated server power; 30 seconds of setup + 0.05 seconds per email. £1,200 hardware over 4 years of continuous operation.
Data: 75 KB per email, plus a 5 MB file in attachment mode (before encoding); two full transfers. One stored copy on an 8 TB, 5 W drive, costing £150 and lasting 4 years. Decimal KB, MB, GB and TB.
02 The calculation
Device electricity25 W × (10 + 0.2 × emails) seconds ÷ 3,600,000 × £/kWh
Server electricity20 W × (30 + 0.05 × emails) seconds ÷ 3,600,000 × PUE ×
£/kWh
Network electricityemails × size in GB × 2 transfers × kWh/GB × £/kWh
Storage electricitytotal TB ÷ 8 TB × 5 W ÷ 1,000 × days × 24 × PUE × £/kWh
Hardware allocationsender hours × £800 ÷ 8,000 hours
+ server hours ×
£1,200 ÷ (4 × 365.25 × 24 hours)
+ stored TB ÷ 8 TB ×
days × £150 ÷ (4 × 365.25 days)
The total is the sum of all five components. Unit cost is total ÷ quantity. Savings compare that unit cost with a one-email batch using the same assumptions. Totals are calculated before rounding.
03 What’s in, what’s out
This estimates one automated batch to one recipient per email, including the sender’s device, allocated delivery compute, two network transfers, one stored copy, and hardware allocation.
It excludes writing and reading time, labour, spam filtering, retries, backups, redundancy, embodied energy, software, buildings, tax, and provider margins. A large batch may span multiple connections in practice; this simplified model shares one setup across the batch. Hardware allocation is an accounting estimate, not a claim that sending an email wears a device by an exact amount.
These boundaries make the calculation inspectable, not universal. This is a starting point for exploring cost, not a provider quote or a carbon-footprint estimate.
04 Notes & references
All numeric defaults are explicit assumptions chosen for this example. They are not sourced measurements or a verified industry average.
For context: the IEA’s overview of data centres and transmission networks ↗ explains why infrastructure efficiency varies. The Green Grid’s PUE guidance ↗ explains the ratio of total facility energy to IT energy. Neither reference validates the defaults here.
Attachment sizes are transferred as entered. Email encodings such as Base64 can increase real traffic. This model does not account for that expansion.