Network Working Group S. Dutta Internet-Draft Independent Intended status: Standards Track 16 September 2025 Expires: 20 March 2026 SIME: Srijal's Integrated Mail Extensions draft-srijal-sime-protocol-00 Abstract This document specifies the SIME protocol, a decentralized, atomic protocol for inter-domain mail transmission and entity-to-entity communication. It defines packet types, headers, MX/SRV-based trust verification, TCP-based delivery, and SIME Extensions for attachments. All servers act as Domain Authorities (DA), and inter- domain transactions are governed by atomic protocol rules. Status of This Memo This Internet-Draft is submitted in full conformance with the provisions of BCP 78 and BCP 79. Internet-Drafts are working documents of the Internet Engineering Task Force (IETF). Note that other groups may also distribute working documents as Internet-Drafts. The list of current Internet- Drafts is at https://datatracker.ietf.org/drafts/current/. 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Dutta Expires 20 March 2026 [Page 1] Internet-Draft SIME September 2025 Table of Contents 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2 2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 2 3. Overview of SIME Protocol . . . . . . . . . . . . . . . . . . 3 4. Packet Types . . . . . . . . . . . . . . . . . . . . . . . . 3 5. Headers . . . . . . . . . . . . . . . . . . . . . . . . . . . 3 6. Authentication and Login . . . . . . . . . . . . . . . . . . 4 7. Message Flow . . . . . . . . . . . . . . . . . . . . . . . . 4 8. Atomic Protocol Rules . . . . . . . . . . . . . . . . . . . . 4 9. Inter-Domain Transactions . . . . . . . . . . . . . . . . . . 5 10. Error Codes . . . . . . . . . . . . . . . . . . . . . . . . . 5 11. Security Considerations . . . . . . . . . . . . . . . . . . . 5 12. MX/SRV Verification . . . . . . . . . . . . . . . . . . . . . 5 13. SIME Extensions for Attachments . . . . . . . . . . . . . . . 6 14. Packet Syntax . . . . . . . . . . . . . . . . . . . . . . . . 6 15. Example Message Flow . . . . . . . . . . . . . . . . . . . . 6 16. Normative References . . . . . . . . . . . . . . . . . . . . 6 Appendix A. Authors' Addresses . . . . . . . . . . . . . . . . . 7 Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 7 1. Introduction SIME (Srijal's Integrated Mail Extensions) is a decentralized protocol designed to provide reliable messaging between users in different Domain Authorities (DA). Each DA manages its own user authentication and registration rules. Atomic protocol enforcement ensures inter-domain transactions follow strict compatibility, reliability, and security rules. All SIME traffic is conducted over TCP to ensure reliable delivery. 2. Terminology DA (Domain Authority) - Server managing a domain and its users ID - Disposable session identifier (e.g., JWT) Transaction ID - Identifier assigned per transaction session TCP - Transmission Control Protocol (mandatory transport) MAIL Packet - Packet containing mail messages CONV Packet - Packet for general communication MX/SRV Record - DNS record or SRV record pointing to server endpoint for inter-domain verification Dutta Expires 20 March 2026 [Page 2] Internet-Draft SIME September 2025 3. Overview of SIME Protocol - Users authenticate with their DA and receive disposable IDs. - Communication is TCP-only to prevent packet loss. - Two primary packet types: CONV and MAIL. - Inter-domain transactions require MX/SRV verification to ensure messages reach the correct DA server. - Atomic rules enforce uniformity; non-compliant servers are rejected. 4. Packet Types CONV Packets: Used for login and general communications: LOGIN START TRANSACTION CONV Figure 1 MAIL Packets: Used for sending messages: PREPARE HEADERS X-Mailed-Type-Render: ; RECIPIENT: user@domain PREPARE MESSAGE END TRANSACTION Figure 2 5. Headers - SENDER: Originating user (user@domain) - RECIPIENT: Destination user (user@domain) - X-Mailed-Type-Render: TXT | MD | HTML - Optional headers may be added via SIME Extensions Dutta Expires 20 March 2026 [Page 3] Internet-Draft SIME September 2025 6. Authentication and Login Users initiate login via CONV packet: LOGIN Figure 3 Server responses: SUCCESS LOGIN : ERROR AUTH Figure 4 Disposable IDs are required for subsequent packets. 7. Message Flow 1. User logs in: CONV Packet → LOGIN → SUCCESS LOGIN : 2. User initiates transaction: CONV Packet → START TRANSACTION 3. Server validates ID: - Success → returns transaction acknowledgment - Failure → returns ERROR AUTH 4. User sends MAIL packet: - PREPARE HEADERS ... - PREPARE MESSAGE 5. User ends transaction: END TRANSACTION 6. Server responds with SENT or appropriate error. 8. Atomic Protocol Rules - No version negotiation; all inter-domain servers must implement the exact protocol. - Non-compliant servers are rejected. - Transactions must be atomic: either all steps succeed or fail. Dutta Expires 20 March 2026 [Page 4] Internet-Draft SIME September 2025 9. Inter-Domain Transactions - DA MX/SRV record must point to verified server endpoint. - Messages are sent only to verified MX/SRV endpoints. - Servers not listed or failing verification are rejected. 10. Error Codes - ERROR AUTH : Invalid login/session - ERROR TRANS : Transaction initiation failure - ERROR HEADER : Invalid or missing headers - ERROR MXVER : Inter-domain MX/SRV verification failure - ERROR PACKET : Malformed packet - ERROR SEND : Message could not be delivered 11. Security Considerations - All packets use TCP for reliable delivery. - Authentication handled per DA; disposable IDs required. - TLS is recommended for inter-domain traffic. - Disposable IDs and transaction IDs mitigate replay attacks. - Inter-domain trust relies on MX/SRV verification; unverified endpoints are rejected. - Confidentiality and integrity of message content require TLS or optional message signing. - Reviewers should note that deployment must account for standard- compliant DNS/SRV usage instead of arbitrary IP:PORT MX records. 12. MX/SRV Verification - Each DA must publish a SIME MX or SRV record specifying its server endpoint. - Inter-domain messages are routed only to verified endpoints. Dutta Expires 20 March 2026 [Page 5] Internet-Draft SIME September 2025 - Unverified endpoints are rejected. 13. SIME Extensions for Attachments - ATTACHMENT: - ENCODING: base64 | hex - Optional metadata headers supported - Attached in content as: 14. Packet Syntax CONV-PACKET = LOGIN-PACKET / TRANSACTION-PACKET / GENERAL-CONV LOGIN-PACKET = "LOGIN" SP USERNAME SP PASSWORD CRLF TRANSACTION-PACKET = "START TRANSACTION" SP ID CRLF / CONV SP PAYLOAD CRLF MAIL-PACKET = "PREPARE HEADERS" SP TRANSACTION-ID SP HEADER-FIELDS CRLF "PREPARE MESSAGE" SP TRANSACTION-ID SP CONTENT CRLF "END TRANSACTION" SP TRANSACTION-ID CRLF USERNAME = 1*(ALPHA / DIGIT / "-" / "_") PASSWORD = 1*(ALPHA / DIGIT / SYMBOL) TRANSACTION-ID = 1*DIGIT HEADER-FIELDS = *(HEADER-NAME ":" SP HEADER-VALUE CRLF) CONTENT = *(OCTET) Figure 5 15. Example Message Flow User DA-A DA-B | LOGIN | | |------------------>| SUCCESS LOGIN | | START TRANSACTION | | |------------------>| TRANS_ID: 67890 | | PREPARE HEADERS | | |------------------>| PROCEED | | PREPARE MESSAGE | | |------------------>| PROCEED | | END TRANSACTION | | |------------------>| SENT | Figure 6 16. Normative References Dutta Expires 20 March 2026 [Page 6] Internet-Draft SIME September 2025 [RFC793] Postel, J., "Transmission Control Protocol", RFC 793, 1981, . [RFC7519] Jones, M., "JSON Web Token (JWT)", RFC 7519, 2015, . [RFC5321] Klensin, J., "Simple Mail Transfer Protocol", RFC 5321, 2008, . Appendix A. Authors' Addresses Srijal Dutta Email: srijaldutta.official+sime@gmail.com Author's Address Srijal Dutta Independent Email: srijaldutta.official+sime@gmail.com Dutta Expires 20 March 2026 [Page 7]