Definition
AS2 is an IETF-specified transport protocol for exchanging structured business data securely over the internet. The message is encrypted and signed with S/MIME at the sender, posted over HTTPS directly to the recipient's AS2 endpoint, and decrypted and verified there. The recipient answers with an MDN; when signed, it proves the message arrived intact. Because transmission is direct between partners, the traditional VAN intermediary — and its volume-based fees — falls away. The prerequisite is a reachable AS2 station with certificate management on both sides.
Why it matters
Transport choice determines a large share of the ongoing operational effort of an EDI connection. AS2 is fast and produces a solid delivery receipt, but requires a permanently reachable endpoint, certificate maintenance and monitoring that notices when messages stall. SFTP is simpler to run but offers no equivalent proof. A VAN takes over operations and partner management in exchange for recurring cost. For companies without a dedicated EDI team, the operational side of AS2 — not the initial setup — is where projects tend to stall.
How it works
Establishing an AS2 connection follows a fixed sequence: both sides exchange AS2 ID, endpoint URL and public certificate, agree encryption and signature algorithms and the MDN mode (synchronous or asynchronous), then run test transmissions before going live. Three things matter in ongoing operation: rotate certificates before they expire, actively monitor for missing MDNs, and define retry behaviour. For Amazon vendors, Amazon supplies the technical parameters during onboarding.
Real-world examples
• A vendor sends the day's invoices as 810 messages over AS2 each evening and receives a signed MDN per transmission, archived as proof of delivery. • An expired certificate on the partner side causes messages to be rejected — without MDN monitoring this only surfaces when purchase orders stop arriving. • A mid-sized manufacturer chooses Amazon-hosted SFTP over AS2 because nobody in-house can maintain certificates and endpoints.
Common pitfalls
• **Certificate expiry:** the most common reason an AS2 connection suddenly goes silent. Expiry dates belong in monitoring, not in a calendar reminder. • **Not evaluating the MDN:** if you never check the receipt, you never learn that messages failed to arrive. The file sits in your outbox and everything looks fine. • **Confusing transport with content:** a successful AS2 transmission only means the file arrived. Whether the partner accepts it functionally is answered by the response message. • **Underestimating reachability:** AS2 requires an endpoint reachable from the outside. That is an IT security decision, not just an EDI one.
Frequently asked
What does AS2 stand for?+
AS2 stands for Applicability Statement 2, a protocol for transmitting EDI messages securely over the internet — encrypted, digitally signed and with an automatic delivery receipt.
What is an MDN in AS2?+
The MDN (Message Disposition Notification) is the recipient's automatic acknowledgement of receipt. In signed form it proves the message arrived complete and unaltered, making it a delivery receipt. It says nothing about whether the recipient accepts the business transaction itself.
What is the difference between AS2 and SFTP?+
Both move EDI files, but AS2 encrypts and signs at the message level and produces a solid delivery receipt via the MDN. SFTP is a secured file transfer without an equivalent receipt, but considerably simpler to set up and operate.
Does Amazon use AS2?+
Yes. AS2 is Amazon's preferred transport method for vendor EDI connections. Amazon-hosted SFTP and connection via a VAN are also supported. Which option is available for a given account is determined by Amazon during onboarding.