Key takeaways
- The four-corner model places four roles between sender and recipient: sender, its access point, the recipient's access point, recipient.
- Sender and recipient never connect directly: their access points do it, like two email providers.
- A single connection to one access point is enough to reach every participant on the network.
- In Belgium, every business is identified for B2B by the 0208 prefix, its enterprise number (CBE).
The four-corner model, the architecture of the Peppol network
When people talk about Peppol, they usually mention the format (Peppol BIS Billing 3.0) and the B2B mandate that takes effect on 1 January 2026 in Belgium. But behind sending an invoice sits a precise architecture: the Peppol four-corner model. It explains how a document leaves your software and arrives, structured, at your customer, without you ever needing to know their IT provider.
The principle fits in one sentence: the sender and the recipient never communicate directly. Between them sit two certified intermediaries, the access points. This article describes the role of each of the four corners, how an invoice finds its recipient, and what this design changes in practice for a Belgian business.
The four corners, one by one
The model owes its name to the four roles it distinguishes. Two are businesses (you and your customer); two are technical providers (the access points). It is that separation that makes the network interoperable.
- 1
Corner 1: the sender
The business that creates the document in its invoicing software. It enters data; it does not write XML.
- 2
Corner 2: the sender's access point
It puts the document into the Peppol format, validates it, looks up the recipient and sends it over the network.
- 3
Corner 3: the recipient's access point
It receives the document, checks its compliance and delivers it to the recipient.
- 4
Corner 4: the recipient
It gets a structured invoice that its accounting can read, with no re-keying.
Corners 1 and 4 are the commercial parties: they decide the content of the invoice. Corners 2 and 3 are the access points: they do not touch the substance, they guarantee that the document travels in the right format, to the right recipient, with proof of delivery. An access point is a provider certified by OpenPeppol, the association that governs the network.
How an invoice finds its recipient
This is the least understood part of the model. To deliver a document, corner 2 has to answer two questions: who is the recipient, and which access point serves them? The Peppol network answers through a two-level directory layer.
The addressing mechanism, step by step
The recipient's identifier
A scheme plus a number. In Belgium, the 0208 prefix designates the enterprise number (CBE), that is the VAT number without the 'BE' prefix and the dots.
The SML (Service Metadata Locator)
A central, DNS-based directory service that tells the sending access point where to find the recipient's information.
The SMP (Service Metadata Publisher)
The directory that publishes, for that recipient, which access point serves them and which document types they accept.
Delivery over AS4
Once the right access point is identified, the document travels from corner 2 to corner 3 using the network's AS4 transport profile.
In concrete terms, a business whose VAT number is BE0123.456.789 is reachable on Peppol at the address 0208:0123456789. Your access point queries the SML, retrieves the address of the recipient's SMP, reads the responsible access point there, then sends. All of this in a few seconds, with no action from you. For the detail of connecting on the business side, see the Peppol access point guide.
Why four corners rather than a direct connection
The value of the model becomes clear as soon as you compare it with the alternative. Without a network, every business would have to negotiate and maintain a technical connection with each of its partners: as many formats, protocols and agreements to manage. The four-corner model replaces that web of bilateral links with a single connection.
| Direct exchange (point-to-point) | Peppol four-corner model | |
|---|---|---|
| Number of connections to set up | One per partner | Just one, to the access point |
| Prior bilateral agreement | ||
| Enforced and validated format | ||
| Reach beyond borders | Limited | The whole Peppol network |
| Standardised proof of delivery |
That pooling has a direct consequence. The network is open: any participant can write to any other, as long as both are connected, without ever having spoken before. That is what sets a four-corner model apart from a closed network, where you can only reach the members of a single platform.
distinct roles
sender, two access points, recipient
connection
to reach the whole network
Belgian scheme
identifies a business by its CBE number
Send your invoices over the Peppol network without managing the technical corners
YouInv handles the format, the routing and the validation. You enter the invoice, the network delivers it.
What the model changes for your business
The good news is the same as for the format: you do not have to handle corners 2 and 3. Your software and your access point take care of addressing, format and proof of delivery. Your role is limited to issuing accurate invoices and making sure your enterprise number is correctly registered on the network.
What the model does change is the criterion for choosing your tool. Issuing a PDF is no longer enough for B2B: your software must be genuinely connected to a Peppol access point, able to send as well as receive. That is the first thing to check when picking or upgrading your solution before the 2026 deadline.
Further reading
- Understanding the Peppol network in 5 minutes: the big picture of the network and its access points.
- The Peppol access point: what it does and how to connect: connection seen from the business side.
- Peppol in Belgium: the B2B mandate on 1 January 2026: who is affected and from when.
What is the Peppol four-corner model?
It is the architecture of the Peppol network. It places four roles between the sender and the recipient of a document: the sender (corner 1), its access point (corner 2), the recipient's access point (corner 3) and the recipient (corner 4). The sender and the recipient never connect directly; their access points exchange the document over the network.
What are the four corners of the Peppol model?
Corner 1: the business that issues the document. Corner 2: its access point, which puts the document into the Peppol format and sends it. Corner 3: the recipient's access point, which receives and validates the document. Corner 4: the recipient, who gets a structured invoice ready to process.
How does an invoice find the right recipient on Peppol?
Each participant is identified by a scheme and a number. In Belgium, the B2B scheme is the 0208 prefix, which designates the enterprise number (CBE). The sender's access point queries the network directory (SML then SMP) to learn which access point serves that recipient and which documents it accepts, then delivers the invoice.
What is the difference between a four-corner model and a direct exchange?
In a direct (point-to-point) exchange, each business has to set up a connection with every one of its partners. In the four-corner model, you connect once to an access point and you reach every participant on the network, with no prior bilateral agreement.
Do I need to understand the four-corner model to send an invoice?
No. Your software and your access point handle corners 2 and 3 for you: routing, format and validation. Knowing the model mainly helps you pick a tool that is genuinely connected to the network and understand what happens when an invoice is delivered.
