AS1
Applicability Statement 1. RFC 3335 specifies secure EDI transport over SMTP using S/MIME.
Definition
AS1 (Applicability Statement 1) is the first specification of the AS family, published by IETF in RFC 3335 in September 2002. It describes how to transport EDI (EDIFACT, X12, XML) as an SMTP email attachment, with S/MIME encryption and signature, signed MDN acknowledgement, and MIC for non-repudiation. AS1 was largely superseded by AS2 but remains defined in some legacy chains.
Origin
AS1 was developed between 1996 and 2002 under the IETF EDIINT (Electronic Data Interchange Internet Integration) working group, authored by T. Harding, R. Drummond and C. Shih. RFC 3335 was published in September 2002. The protocol was designed to work with any existing SMTP MTA, which allowed companies to reuse their existing email infrastructure.
Example in context
A typical AS1 exchange starts with an email From: edi@partner.com, To: edi@hub.com, with an S/MIME payload attached containing an encrypted and signed ORDERS purchase order. The receiver responds with a signed MDN containing the SHA-1 MIC of the received message, itself sent as a return email. The average latency (5-30 minutes) tied to SMTP routing pushed the industry to migrate to AS2 over HTTPS.