A system and method are disclosed for transparently providing certificate validation and other services without requiring a separate service request by either a relying customer or subscribing customer. In a preferred embodiment, after the subscribing customer digitally signs a document (e.g., a commercial document such as a purchase order), it forwards the document to a trusted messaging entity which validates the certificates of both the subscribing customer and relying customer and the respective system participants of which they are customers. If the certificates are valid, the trusted messaging entity appends a validation message to the digitally-signed document and forwards the document to the relying customer. A validation message is also preferably appended to a digitally-signed receipt from the relying customer and transmitted to the subscribing customer. In this way, both the relying customer and subscribing customer obtain certification of their respective counterparty to the transaction.