PEPPOL: Complete Definition and Guide

What is PEPPOL?

PEPPOL, which stands for Pan-European Public Procurement OnLine, is a standardized communication network designed to facilitate the exchange of electronic commercial documents between organizations, both public and private. Initially developed by the European Commission to harmonize digital public procurement, PEPPOL has become the reference infrastructure for electronic invoicing in a growing number of European countries and beyond.

The PEPPOL network functions as a universal communication standard for commercial documents. It can be compared to the telephone network: regardless of the sender's and recipient's operators, the message reaches its destination through a common protocol. Similarly, a company connected to the PEPPOL network through any certified access point can exchange documents with any other company on the network, regardless of their access point.

In Belgium, PEPPOL has been chosen as the reference network for mandatory B2B electronic invoicing from 2026. This decision places Belgium at the forefront of European countries in terms of digitalizing commercial exchanges. KERN-IT, as the developer of PeppolOutbox, is a direct participant in this ecosystem with a certified and operational PEPPOL access point.

Why PEPPOL Matters

PEPPOL's importance lies in its ability to solve a fundamental problem in digital document exchange: interoperability. Without a standardized network, each pair of companies would need to negotiate their own format and exchange channel, creating exponential complexity. PEPPOL provides an elegant solution to this problem:

• Universal interoperability: a single connection to a PEPPOL access point is sufficient to exchange with all millions of network participants across Europe and beyond (Australia, Singapore, New Zealand).
• Format standardization: PEPPOL mandates document specifications (Peppol BIS) based on the UBL format, ensuring every invoice, purchase order or credit note is structured identically and processable by all systems.
• Enhanced security: the AS4 transport protocol used by PEPPOL ensures encryption, authentication and non-repudiation of exchanges. Every document is digitally signed and its delivery is confirmed by an acknowledgment.
• Regulatory compliance: using PEPPOL for electronic invoicing automatically guarantees compliance with Belgian and European legal requirements, as the network is designed to meet these regulations.
• Growing network: with over 300,000 entities registered in the PEPPOL Directory and sustained monthly growth, the network has reached a critical mass making it an essential standard.

How It Works

PEPPOL's technical architecture is built on the four-corner model, which is at the heart of the network's operation. This model involves four actors for each document exchange:

The first corner is the sender (Corner 1), the company issuing the document. The second corner is the sender's access point (Corner 2), a certified provider that takes charge of the document, validates it and transmits it on the network. The third corner is the recipient's access point (Corner 3), another certified provider that receives the document and delivers it to the fourth corner, the final recipient (Corner 4).

This model presents a decisive advantage: each company only needs to connect to a single access point to reach the entire network. Document routing is handled by the SML (Service Metadata Locator) and the SMP (Service Metadata Publisher), two infrastructure components that enable each access point to automatically discover the recipient's access point from their PEPPOL identifier.

A Belgian company's PEPPOL identifier is typically based on its BCE enterprise number (scheme 0208). When an access point receives a document to send, it queries the SML to locate the recipient's SMP, then the SMP to obtain connection information for the recipient's access point. The document is then transmitted via the AS4 protocol, which ensures TLS encryption, digital signature and delivery confirmation.

Documents exchanged on PEPPOL comply with Peppol BIS (Business Interoperability Specifications), which define the exact structure of each document type: invoice (BIS Billing 3.0), purchase order (BIS Ordering 3.0), catalogue (BIS Catalogue 3.0), and more. These specifications are based on the UBL 2.1 format with specific validation rules ensuring each document contains all required information in the correct format.

Concrete Example

Let us illustrate PEPPOL's operation with a real case. Company A, an office supplies provider in Brussels, needs to send an invoice to Company B, a law firm in Liege. Company A uses KERN-IT's PeppolOutbox as its access point, while Company B is connected through a different certified access point.

Company A creates its invoice in its accounting software. Via the PeppolOutbox API, the invoice is automatically converted to Peppol BIS Billing 3.0 format and submitted to the access point. PeppolOutbox validates the document (structure, mandatory fields, amount consistency), then queries the SML to locate Company B's access point. The document is transmitted within seconds via AS4, and PeppolOutbox receives an acknowledgment confirming delivery.

On Company B's side, the invoice automatically appears in their system with all structured data ready for accounting integration: invoice number, date, line items, net and gross amounts, VAT and references. No manual data entry is required. The complete process from issuance to reception takes less than 30 seconds.

Implementation

1. Obtain a PEPPOL identifier: the identifier is based on the BCE enterprise number (scheme 0208:BCE_number). Registration is done through the chosen access point.
2. Choose a certified access point: select a PEPPOL Access Point certified by OpenPEPPOL. KERN-IT's PeppolOutbox offers a solution tailored to the Belgian market with French/Dutch interface and local support.
3. Configure technical integration: connect accounting software to the access point. PeppolOutbox provides a documented RESTAPI, CSV import and a manual web interface to accommodate all levels of technical maturity.
4. Register capabilities in the SMP: declare in the Service Metadata Publisher the document types the company can receive (invoices, credit notes), allowing other participants to automatically discover these capabilities.
5. Perform end-to-end testing: send and receive test invoices with pilot partners to validate the complete chain before going live.
6. Go to production: switch real exchanges to PEPPOL progressively, starting with the most receptive business partners.

Associated Technologies and Tools

• AS4 (Applicability Statement 4): the secure transport protocol used by PEPPOL for document transmission, ensuring encryption, mutual authentication and delivery acknowledgment.
• UBL 2.1 (Universal Business Language): the standard XML format for structured commercial documents that forms the basis of Peppol BIS specifications.
• SML/SMP (Service Metadata Locator/Publisher): PEPPOL's network discovery infrastructure enabling automatic document routing to the correct recipient access point.
• Python and Django: technologies used by KERN-IT to develop PeppolOutbox, enabling robust XML document processing, secure certificate management and a performant REST API.
• PostgreSQL: a database for compliant archiving of exchanged documents and routing metadata management.
• Docker: containerization facilitating deployment and high availability of the PEPPOL access point.

Conclusion

PEPPOL is far more than a technical network: it is the infrastructure that makes large-scale electronic invoicing possible across Europe. Its four-corner model design, rigorous standardization and built-in security make it the most robust and scalable solution for commercial document exchange. With Belgium's 2026 obligation, every company must prepare to join the PEPPOL network. KERN-IT, through PeppolOutbox, provides a simple and reliable entry point into this ecosystem, with the technical expertise of a developer who masters the protocol from end to end.