Preamble / Disclaimer

Peppol is designed so that such information is no longer a prerequisite for electronic invoicing. The document transmission mechanism in the Peppol framework is based on registers of reception capacities, publicly consultable online at any time, and which allow the senders of documents to discover in which format their recipient is able to receive them and this in real time (in fact a request to the SML which redirects to the corresponding SMP).  The consultation of these registers is the business of the invoicing software, not of those who use them. 
However, during the first years of Peppol's deployment, as long as (1) this mechanism is used in a confidential manner and (2) a limited number of recipients are actually registered in these registers, it is understandable that companies exchanging invoices want to know this information in advance. This is why several more traditional mechanisms exist (websites).

On a Belgian scale - smp.belgium.be

In 2016, in order to facilitate the adoption of e-billing in Belgium, the authorities set up a national register, smp.belgium.be. The content of the register can be consulted on the following page: https://digital.belgium.be/e-invoicing/PeppolSearch.html
Between 2016 and 2021, (almost) all Peppol invoice recipients were centrally registered there, as the use of this register was compulsory for all Belgian companies. Since 2019, the obligation has been abolished, but most companies (or more precisely their IT providers) have continued to use it. This is likely to be less and less the case, as IT solutions evolve, because the abolition of the obligation to use the central register is the result of a demand from this sector, motivated by its negative technical (and therefore financial) impact.  As a result, more and more Belgian companies will be registered in other registers (there are more than 80 of them). They will therefore no longer appear on this page - but in the Peppol Directory (see next point). 

In Europe and worldwide - Peppol Directory 

Since the end of 2018, https://directory.peppol.eu offers a similar possibility but for all Peppol document recipient registers. 

The complete list of the Peppol directory can even be downloaded using the following link: https://directory.peppol.eu/public/locale-en_US/menuitem-search. click on "Download all [XML]" 

Peppol Directory also provides a web service that allows you to obtain a list of recipients based on filters. This web service is explained on the following page: https://directory.peppol.eu/public/locale-en_US/menuitem-docs-rest-api.

Notes:

• The use of the above web service should obviously not replace the standard mechanism for discovering the "receiving capabilities" of participants, specified by the Peppol framework.
• Only those participants who have requested it are listed in the Peppol Directory. The list in the Peppol Directory is therefore not exhaustive - but it is nevertheless very complete.