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, but not via a central authority) |
Post-audit system (introduction of a clearance-like system called "PPF" planned by 2026) |
Mixed system: Suministro Inmediato de Información (SII) = almost real-time reporting, but invoices go directly between companies |
Post-audit system |
| Role of the tax authority |
Central point of contact: SDI checks and forwards |
Only indirectly involved: invoices go directly between companies, reports via advance returns/declarations |
No central point of contact to date; central platform for forwarding planned for the future |
Tax administration receives transaction data in near real time (SII), but is not involved in the transmission |
No central office, only obligation to provide data for audits |
| Time of inspection |
Real-time check before delivery |
Downstream for audits and advance notifications |
Downstream, but reform towards real time from 2026 |
Near real time: data must be reported to the tax office within 4 days |
Downstream, only in the context of checks |
| Transmission channels |
PEC, web portal, API/web services, FTP – always to SDI |
Multiple (EDI, e-mail, ZUGFeRD, PDF) |
Multiple (EDI, PDF, Factur-X), central platform in future |
Directly to business partners + parallel notification to SII system |
Multiple (EDI, XML, UBL, PDF) |
| Format |
Uniform XML (FatturaPA) |
Multiple standards (ZUGFeRD, XRechnung, PDF) |
Multiple standards, planned: harmonised XML via PPF |
Free, but notification to SII in structured XML |
UBL-based, no uniform requirement |
| Advantage for tax administration |
Complete control in real time |
Lower technical complexity |
Flexible, planned reform increases transparency |
High transparency through SII reports |
Minimal intervention, focus on personal responsibility |
| Disadvantage for companies |
Mandatory SDI connection, no direct dispatch |
Different formats depending on partner/authority |
Obligation to adapt to new PPF system from 2026 |
Double burden: invoice + report to SII |
Different formats, no uniform specifications |
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: Are the identification details of the supplier and customer, invoice number, date, description, amounts and VAT present?
- Existence of tax numbers: Are the tax numbers of the supplier and customer listed in the Italian tax register?
- Delivery address: Is an electronic delivery address (recipient code or PEC address) specified?
- Amount consistency: Do the calculated figures for the amount, tax rate and VAT match?
- Duplicates: Duplicate invoices are rejected.
2.3 SdI feedback and delivery methods
After an invoice has been submitted, the SdI informs the invoice issuer of the status:
- Delivery confirmation ("Ricevuta di consegna"): Successful verification and delivery; includes date and time. Duration: a few hours to five calendar days.
- Confirmation of non-delivery ("Ricevuta di impossibilità di consegna"): In the event of technical problems (e.g. full PEC mailbox), the invoice is made available in the "Fatture e Corrispettivi" portal. The sender must inform the customer. The invoice is considered issued for the supplier, but only received by the customer once they have accessed it in the portal.
- Confirmation of rejection ("Ricevuta di scarto"): In the event of errors, the invoice is rejected and is considered not to have been issued. Correction and resubmission within five calendar days is required.
Three delivery methods must be specified in the electronic invoice:
- Recipient code: Seven-digit alphanumeric code of the recipient service.
- PEC address: If used, "0000000" must be entered in the recipient code field and the PEC address in the PEC destinatario field.
- "0000000": If no specific address has been communicated, "0000000" is entered in the recipient code field and the SdI makes the invoice available on the "Fatture e Corrispettivi" portal.
Companies can register their preferred receiving channel (PEC or recipient code) once in the "Fatture e Corrispettivi" portal. The SdI then ignores the invoice address and always delivers to the registered channel.
2.4 Definition of terms: Codice Destinatario, Codice SDI and Codice Univoco
- Codice Destinatario and Codice SDI are synonyms. They refer to the seven-digit alphanumeric code for receiving invoices between private companies (B2B and B2C). It is provided by software companies.
- The Codice Univoco is a separate, six-digit code that is used specifically for the transmission of electronic invoices to public authorities.
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.