1. Introduction
Since 1 January 2019, electronic invoicing has been mandatory in Italy for most transactions between companies, freelancers and private individuals based in Italy. Invoices are only valid if they have been sent to the SDI and accepted by it; an invoice sent directly to the customer is therefore no longer a legally valid document. The Sistema di Interscambio (SdI), a central IT system, acts as a "digital postman" for processing and forwarding electronic invoices. This article explains the crucial role and functioning of the SdI in Italian accounting.
2. Main section
2.1 What is the Sistema di Interscambio (SdI)?
The SdI is an IT system managed by the Italian revenue agency (Agenzia delle Entrate). It was introduced in 2008 for mandatory electronic invoicing to public institutions (FatturaPA) and, since 2019, has also been responsible for transactions between private companies (B2B), B2C and with the public administration (PA). It acts as a "virtual postman" that ensures the secure and standardised flow of invoice data.
In Italy, the SDI plays a very central role: it is not only a technical intermediary, but also a supervisory authority. Every invoice must pass through the SDI before it reaches the recipient. This gives the Agenzia delle Entrate immediate access to all transactions in a structured form. This model – often referred to as a "clearance system" – enables near real-time control of VAT data and is strongly focused on combating tax fraud.
In other European countries, on the other hand, the "post-audit system" is usually used. There, companies send their invoices in electronic form directly to their business partners without the involvement of a central authority. The tax authorities only access the invoice information for the purpose of checks or through periodic reports (e.g. advance return for tax on sales, purchases, SAF-T files, SII in Spain). In other words, the authorities carry out checks retrospectively, whereas in Italy the checks are carried out before the invoice is delivered.
The difference therefore lies in the role of the tax administration: while in Italy the SDI is effectively the bottleneck through which every invoice must pass, in most other EU countries communication between companies remains decentralised and is only reported to the tax office on a supplementary basis. Italy thus places greater emphasis on transparency and real-time data, while other countries allow companies more flexibility in transmission and the tax authorities are only involved at a later stage.
Here are some country examples, as of 09/2025:
| Feature |
Italy (SDI) |
Germany |
France |
Spain |
Netherlands |
| Model |
Clearance system |
Post-audit system (planned by 2028: mandatory e-invoicing, no central authority) |
Post-audit system (PPF clearance-like system planned by 2026) |
Mixed system: SII (near real-time reporting) |
Post-audit system |
| Role of the tax authority |
Central point: SDI checks and forwards |
Indirect involvement only |
No central hub yet; central platform planned |
Receives data in near real time (SII) |
No central office |
| Time of inspection |
Real-time before delivery |
Downstream (audits) |
Downstream, real-time reform from 2026 |
Near real-time (4 days) |
Downstream |
| Transmission channels |
PEC, portal, API/web services, FTP |
Multiple (EDI, e-mail, PDF, ZUGFeRD) |
Multiple (EDI, PDF, Factur-X) |
Direct + SII parallel reporting |
Multiple (EDI, XML, UBL) |
| Format |
XML (FatturaPA) |
Multiple: ZUGFeRD, XRechnung, PDF |
Multiple, harmonised XML planned |
Structured XML (SII) |
UBL-based |
2.2 The core functions of the SdI in Italy: Receipt, verification and forwarding
The SdI fulfils three main functions:
- Receipt: It accepts electronic invoices exclusively in the legally prescribed XML format.
- Verification: It performs automatic checks on these XML files.
- Forwarding: After successful verification, it forwards the invoices to the intended recipients.
The SdI ensures the authenticity and integrity of the XML files by checking the format, size and (optionally) the digital signature. The invoice issuer remains responsible for the tax correctness of the content.
The verification includes detailed checks:
- Mandatory information (supplier, customer, invoice number, date, description, amounts, VAT)
- Existence of tax numbers
- Electronic delivery address (recipient code or PEC)
- Amount consistency
- Duplicate invoices
2.3 SdI feedback and delivery methods
After an invoice has been submitted, the SdI informs the invoice issuer of the following statuses:
- Delivery confirmation ("Ricevuta di consegna"): Successful verification and delivery.
- Confirmation of non-delivery ("Ricevuta di impossibilità di consegna"): Invoice is available in the “Fatture e Corrispettivi” portal.
- Confirmation of rejection ("Ricevuta di scarto"): Invoice rejected; must be corrected and resubmitted.
Delivery methods:
- Recipient code
- PEC address (with “0000000” in the code field)
- “0000000” for portal delivery
Companies can register their preferred receiving channel in the portal; the SdI will always use this channel.
2.4 Definition of terms: Codice Destinatario, Codice SDI and Codice Univoco
- Codice Destinatario / Codice SDI: Seven-digit alphanumeric code for B2B/B2C invoices.
- Codice Univoco: Six-digit code for public administration invoices.
3. Conclusion
The Sistema di Interscambio is a central pillar of the Italian tax system, which automates, standardises and checks compliance with electronic invoicing. Understanding how it works is essential in order to comply with legal obligations and leverage the efficiency of digital processes.