The SML (Service Metadata Locator) is the central DNS-based directory of the PEPPOL network. Its job is simple: given a PEPPOL participant ID, tell the sender which SMP (Service Metadata Publisher) holds that participant's routing metadata.
The SML doesn't store routing details itself — it only stores a pointer to the right SMP. The full lookup chain works like this:
- Sender has the receiver's PEPPOL ID (e.g.
0184:CHE123456789) - Sender queries the SML (DNS lookup) → gets the hostname of the receiver's SMP
- Sender queries that SMP → gets the receiver's access point endpoint URL and supported document types
- Sender delivers the document directly to that access point via AS4
This design means no central message broker is involved — once the lookup is done, document exchange is point-to-point between access points. The SML just makes discovery possible without a central routing hub.
Key facts
- Operated by: OpenPEPPOL (and mirrored by the European Commission for EU public procurement)
- Technology: DNS — participant IDs are hashed and resolved as DNS hostnames
- Role: pointer directory only — stores SMP location, not routing data
- Works with: SMP (which holds the actual endpoint data)
- PEPPOL ID format used in lookups: scheme +
::+ value (e.g.0184::CHE123456789)