Internet-Draft Email over Bundle Protocol January 2023
Blanchet Expires 21 July 2023 [Page]
Internet Engineering Task Force
Intended Status:
Standards Track
M. Blanchet

Encapsulation of Email over Delay-Tolerant Networks(DTN) using the Bundle Protocol


This document describes the encapsulation of emails using RFC5322 format in the payload of bundles of the Bundle Protocol for the use case of Delay-Tolerant Networks(DTN) such as in space communications.

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This Internet-Draft will expire on 21 July 2023.

Table of Contents

1. Introduction

An important use case of Delay-Tolerant Networks(DTN) using the Bundle Protocol[RFC9171] is in space communications. Current scenarios by space agencies involves the use of an IP network on the planetary body and the use of the Bundle Protocol between planetary bodies, including Earth. Therefore, there are IP endpoints at both ends, and then bundles could be used as a transport of Internet related application payload. This document describes the encapsulation of emails over bundles so that end-users on the remote end (aka on a planetary body such as Moon or Mars) or processes can use typical Internet Email software and tools to use emails, while the emails when transiting in space is encapsulated into bundles of the Bundle Protocol.

It should be noted that in DTNs, delays may be very large compared to normal delays on (Earth) Internet. Therefore, the SMTP [RFC5321] "conversation" between the two SMTP peers should be avoided since it will take many round-trips over long delays networks to achieve the delivery. Therefore, this document proposes to encapsulate the whole Email using the Internet Message Format[RFC5322] as a single file into bundles of the Bundle Protocol.

1.1. Requirements Language

The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in BCP 14 [RFC2119] [RFC8174] when, and only when, they appear in all capitals, as shown here.

1.2. Vocabulary

2. Description

In a typical scenario, the email would be created on (Earth) Internet, sent using regular delivery (DNS MX records, SMTP, ...) to a destination address that points to a location on a planetary body. That email would arrive to an SMTP server which is connected to the Bundle agent[RFC9171] capable of routing bundles to the final Bundle agent on the other planetary body, who has also a connection to an SMTP server. That SMTP server on the other planetary body is responsible for final delivery on that planetary body network. The target bundle protocol service number contained in the bundle is the one allocated by IANA per this document.

TBD: artwork representation

This document assumes that there is a close interaction between a Mail Transfer Agent(MTA) and a Bundle protocol agent, in, for example, the form of interprocess communication. However, the specific interaction is outside the scope of this document and is left to the implementation.

3. Encapsulation

The payload of the bundle [RFC9171] is an Internet Message Format [RFC5322]. A bundle can only contain a single email.

If the email is too large to fit in a single bundle, then the bundle agent uses bundle fragmentation as described in section 5.8 of RFC9171 to slice the email into multiple bundles. It is the responsability of the receiving bundle agent to properly reassemble the multiple bundle payloads into the source email.

The receiving bundle agent will receive the email-containing bundle(s) on this document specifically assigned IANA service number. The agent transfers the email in [RFC5322] format to a Mail Transfer Agent(MTA) that will deliver to the appropriate location as normal practice on Internet.

4. Considerations

Configuring and deploying an isolated IP network on a planetary body with local mail servers, DNS servers and email client needs careful consideration. For example, emails sent between two end-users on the same planetary body should not go through space links down to Earth and back to the planetary body. This operational consideration is not described here and is outside the scope of this document.

By using the encapsulation of emails using the [RFC5322] format, there is no negotiation and no declaration of capabilities as it is done in normal SMTP[RFC5321]. Therefore, the source endpoint has no way by this solution to know the capabilities of the other endpoint. Therefore, on the target planetary bodies MTAs should be properly configured to receive the appropriate kind of emails sent from another planetary body. As with SMTP, it is very possible that either improper configuration or other reasons cause the destination MTA to reject the email. In this case, it should send an error using the same technique on the reverse path, if at least the From address is parsable. If the email is not parsable on the destination MTA, then normal operational logging shall be used. Similarly to the previous paragraph, this consideration of non-negotiation of capabilities is not described here and is outside the scope of this document. It is however expected that this environment will be highly configured and managed ans such issues shall not be typical.

5. IANA Considerations

This document requests IANA to allocate a new Bundle Protocol service number under the current CBHE Service Numbers and assign it to this document. Description should be: "RFC5322 content (aka Email)"

Note to IANA (to be removed by the RFC editor): prefer 25 to relate to the Internet email service, but not a big deal if not.

6. Security Considerations

Sending any payload with bad data over a space link is a somewhat DOS attack. It is expected that this environment will be highly managed and controlled, therefore, before a bundle is sent, the payload is properly verified and access control to the space network will be tightly controlled.

7. References

7.1. Normative References

Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, DOI 10.17487/RFC2119, , <>.
Resnick, P., Ed., "Internet Message Format", RFC 5322, DOI 10.17487/RFC5322, , <>.
Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC 2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174, , <>.
Burleigh, S., Fall, K., and E. Birrane, III, "Bundle Protocol Version 7", RFC 9171, DOI 10.17487/RFC9171, , <>.

7.2. Informative References

Klensin, J., "Simple Mail Transfer Protocol", RFC 5321, DOI 10.17487/RFC5321, , <>.



Author's Address

Marc Blanchet