About AS2

AS2 (Applicability Statement 2) is a specification describing how to transport structured business-to-business (B2B) data securely and reliably over the Internet. Security is achieved by using digital certificates and encryption.

AS2 uses the HTTP(S) protocol to transmit data and supports S/MIME encryption and digital signatures for the payload. The payload is sometimes referred to as the "message" or "document". Message encryption and signing are separate from HTTPS transport encryption.

AS2 is a peer-to-peer (P2P) protocol where both sides of the connection need to agree to the connection and provide each other with the required information for successful data transmission. These connections are sometimes referred to as "AS2 partnerships".

AS2 was designed for business-to-business transactions, such as Purchase Orders, Invoices, Shipment Statuses, and other business documents, so the two businesses at either end of the AS2 connection are referred to as trading partners.

About Message Disposition Notification (MDN)

A Message Disposition Notification (MDN) is a digital receipt, returned by the receiver of the AS2 payload (message), to provide confirmation of delivery to the sender.

The MDN can return a successful delivery notification or a failure outcome. A failed MDN typically contains details about why the delivery failed.

For successfully processed incoming messages, Files.com returns a signed MDN containing a Message Integrity Check (MIC) in the Received-Content-MIC field. The MIC lets the sending partner compare the received content with what they sent. Files.com includes it for signed and unsigned messages, with or without S/MIME message encryption.

A valid MDN signature lets the sender verify that the receipt came from the receiving AS2 identity. Together with the MIC, it provides evidence of the content received, which helps trading partners reconcile delivery records. It does not mean that the original message was signed or that its signature was validated. The partner's incoming signature validation level controls that separate check.

MDNs are optional in the AS2 protocol, but they are widely adopted and often required by trading partners. You can view incoming and outgoing MDNs in the AS2 Logs.