Email

Assessment of a message, campaign or email volume distinguishes writing, reading, transfers and retention. A universal per-email figure would conceal differences in size, recipients and storage duration.

Prepare the data

Input	Coverage
Messages, recipients and reading rate	Campaign or period activity
Message size	Body, attachments and actual transmitted data
Writing and reading durations	Device time, separate from server processing
Physical copies and retention	Storage, backups counted once
Hosting	Allocated processing, excluding separately assessed storage

The scenario assumes average recipient behaviour. For annual email usage with an existing archive, that archive forms part of the storage inventory; new-message count does not describe it.

Device time is messages × (writing time + recipients × reading share × reading time). Electricity and allocated manufacture rely on duration converted to hours.

The transfer model adds one upload, one delivery per recipient and readers' downloads. This is a simplified path; measured flows replace it if synchronization or protocols differ.

Detailed method and special cases

Break down a message journey

Stage	Activity	Check
Composition	Sender's active time	Once per composed message, not per recipient
Sending and delivery	Message, attachments, envelopes and recipients	Logical messages distinct from transferred bytes
Reading and synchronization	Reading share, duration, downloads and devices	Synchronization may occur without reading
Retention	Physical capacity and duration, copies and backups	Replication counted once, including any factor coverage
Processing	Spam filtering, antivirus, indexing, mail server	Shared-resource allocation

For $N$ messages, $R$ recipients, reading share $l$, writing/reading minutes $t_e,t_l$ and size $s$ in MB:

$$H_{device}=\frac{N(t_e+Rl t_l)}{60}$$ $$G_{network}=\frac{Ns}{1000}(1+R+Rl d),\qquad S_{storage}=\frac{Ns}{1000}c m$$

$d$ is downloads per reader, $c$ total physical copies and $m$ months. This synchronization model is simplified: clients downloading every message require measured bytes or an adapted journey that distinguishes reading and download shares.

Device manufacture uses the average per-second profile or, in custom mode, device manufacture divided by lifetime. The storage factor in kg CO₂e/GB.month must cover its stated phases. Hosting excludes storage when calculated separately.

Marketing campaigns, old mail and attachments

Campaign composition forms a separate contribution or a share of time allocated among sent messages.

Email campaign activities

1. 1 compositionMessage creation
2. 1,000 sendsDistribution
3. 250 readingsReader activity

Composition is counted once for the campaign.

Fictitious scenario. Tracking-pixel opens do not measure reading time. Storage, attachments and processing complete the inventory.

Annual mailbox storage includes existing mail. Integrate capacity over time, for example monthly average capacity times duration. The simulator represents a batch retained for a fixed period; it does not reconstruct mailbox history.

A download link replaces an attachment with other transfers and remote storage. The assessment covers actual accesses, retention and the sharing service. The effect depends on reader count; no fixed saving is assumed.

Sender, recipients and mail protocols

The historical journey distinguishes the sender device, sending server, receiving server and recipient device. Each segment may involve a different country and network. Header exchanges, IMAP synchronisation and POP downloads cannot be inferred from the reading rate alone.

Sent copies, received copies and backups may have different retention periods. Their physical capacity is tracked separately before aggregation in GB.months. The example's single retention parameter is a simplification, not a rule shared by all mailboxes.

The historical note relies on ADEME Impact CO₂'s hosting approach. The example below uses separate processing and storage inputs: it does not reproduce that generic estimate. Complete factors and their components are never added together.

Interpret the result

Example: default inputs give 46.67 device hours, 2.8 GB transferred and 36 GB.month stored. Missing network and storage factors prevent a complete total. The result distinguishes measurements, inferences and exclusions and relates to a sent message or clearly defined campaign.

Complete the boundary

Network and storage factors remain blank until compatible data is supplied. The subtotal does not treat them as zero. Campaign creation, CRM and analytics tools should be added if the studied function includes them.

A complete email-service factor already includes its components. Within a collaboration suite, the email share requires documented allocation. A published figure is insufficient without checking its period, boundary and unit.

The result is framed by boundary and functional unit, allocation and double counting.

Electricity factors come from the D4B 2025 snapshot¹. Prefilled activity and hosting values are exercise assumptions. Factors and conventions are available below the simulator.

Attachment size and retention duration affect traffic and storage differently. Deleting messages reduces an allocated quantity here; it does not prove an immediate reduction in electricity consumption on a server that remains powered on.

Interactive example

This example applies the calculations and limitations described above.

Ex: 1,000 messages of 1 MB stored as three physical copies for twelve months represent 36 GB.month. This is activity, not a carbon footprint. The storage factor must apply to physical capacity and cover the declared phases.

Example inputs

Messages sentRecipients per messageMessage and attachment size (MB)Retention period (months)Total stored physical copiesUser deviceMobile / computer mixComputer: 60% laptop, 40% desktopMobile: 95% smartphone, 5% tabletLaptop (illustrative configuration)Desktop with display (illustrative configuration)Smartphone (illustrative configuration)Tablet (illustrative configuration)Custom parametersUser countryFranceGermanyUnited StatesUnited KingdomChinaIndiaPolandSwedenNorwayJapanBrazilAustraliaTaiwanSouth KoreaIrelandHosting countryFranceGermanyUnited StatesUnited KingdomChinaIndiaPolandSwedenNorwayJapanBrazilAustraliaTaiwanSouth KoreaIreland

Adjust assumptions

Writing time (min)Reading time (min)Share of recipients who read (%)Downloads per readerStorage, manufacture and operation included (kg CO₂e/GB.month)Allocated IT energy over the period (kWh)Allocated hosting manufacture over the period (kg CO₂e)Site PUECellular traffic share (%)Fixed network factor, complete path (kg CO₂e/GB)Cellular network factor, complete path (kg CO₂e/GB)

Calculated subtotal24.02 kg CO₂e

0.02402 kg CO₂e / sent message

Not assessed: Missing storage factor ; Missing fixed network factor ; Missing cellular network factor ; Unlisted third-party services and building manufacture.

Result and activity breakdown

Contribution	kg CO₂e
Retained storage	Not assessed
Device: allocated manufacture	0.158
Device: electricity · 0.8223 kWh	0.02625
Fixed network	Not assessed
Cellular network	Not assessed
Hosting: allocated manufacture	20
Hosting: electricity · 120 kWh	3.831

• Cumulative physical storage : 36 GB.month
• Cumulative device time : 46.67 h
• Transfers : 2.8 GB

Prefilled activity and hosting values are example assumptions. The result covers climate impact; unassessed contributions remain identified.

Simulator factors and conventions

Electricity: D4B 2025 national averages. Use country does not change manufacture. Network factors remain unknown until supplied; they must cover the full path, manufacture and operation included. In this illustration, the distance from the D4B per-GB·km model is incorporated upstream into the per-GB route factor.

Devices: illustrative parametric configurations. Profiles are calculated from components and include their display. Computer and mobile groups assume 60% laptops and 95% smartphones, weighted by active time. These are fictional compositions, not measured averages. Manufacturing per second is already allocated over lifetime.

Current profile : 17.62 W · 0.003385 kg CO₂e/h allocated manufacture.

Manufacturing is allocated over calendar lifetime (8,760 h/year). Custom inputs replace the calculated profile; they are not added to it.

The storage factor covers the specified copies and duration. Hosting must exclude that same storage to avoid double counting.

Footnotes

1. Digital4Better, D4B 2025 snapshot. Snapshot 77cae4a, 2025 data; reviewed 16 October 2026. ↩