Deploying and Using Email in Deep Space
draft-many-tiptop-email-00

Internet Engineering Task Force                              M. Blanchet
Internet-Draft                                                  Viagenie
Intended status: Informational                              21 July 2025
Expires: 22 January 2026

                Deploying and Using Email in Deep Space
                       draft-many-tiptop-email-00

Abstract

   This document is an assessment on the email protocols to be used in
   deep space and provides recommendations to deploy and use email in
   deep space.

Status of This Memo

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   This Internet-Draft will expire on 22 January 2026.

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Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
     1.1.  Requirements Language . . . . . . . . . . . . . . . . . .   2
     1.2.  Document and Discussion Locations . . . . . . . . . . . .   2
   2.  Assessment  . . . . . . . . . . . . . . . . . . . . . . . . .   3
   3.  Deployment Recommendations  . . . . . . . . . . . . . . . . .   3
   4.  Discovering the Next Mail Server  . . . . . . . . . . . . . .   4
   5.  Transport Considerations  . . . . . . . . . . . . . . . . . .   5
   6.  DNS Considerations  . . . . . . . . . . . . . . . . . . . . .   5
   7.  Unwanted Email Considerations . . . . . . . . . . . . . . . .   5
   8.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   5
   9.  Security Considerations . . . . . . . . . . . . . . . . . . .   5
   10. References  . . . . . . . . . . . . . . . . . . . . . . . . .   5
     10.1.  Normative References . . . . . . . . . . . . . . . . . .   6
     10.2.  Informative References . . . . . . . . . . . . . . . . .   6
   Acknowledgements  . . . . . . . . . . . . . . . . . . . . . . . .   7
   Author's Address  . . . . . . . . . . . . . . . . . . . . . . . .   7

1.  Introduction

   Deep space communications involve long delays (e.g. Earth to Mars is
   4-22 minutes) and intermittent communications, because of orbital
   dynamics.  As discussed in [I-D.many-tiptop-ip-architecture], IP
   packets are stored by forwarders facing intermittent links, instead
   of dropping them.  So packets travelling from Earth to a celestial
   body surface network may take a long time to arrive at destination,
   such as minutes, hours, days, weeks.  The QUIC transport protocol,
   profiled for space delays, is used for reliable transport.

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.  Document and Discussion Locations

   The source of this document is located at
   https://github.com/marcblanchet/draft-tiptop-email.  Comments or
   changes are welcomed by filing a PR or an issue against that
   repository.

   This subject should be discussed on the IETF tiptop working group
   mailing list.

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2.  Assessment

   On Internet, to forward an email from the sender to the receipient
   server, the SMTP protocol is used over TCP.  Prior to sending, the IP
   address of the recipient server is found by quering the MX records
   and then the IP address records (A, AAAA) of the MX returned values.
   SMTP goes through a series of messages between the client and the
   server to exchange capabilities, sender and recipient email addresses
   and then content of the email.  These multiple exchanges result to
   multiple RTT to send the whole email.  To get its email, a user uses
   IMAP or POP, both over TCP, or a web interface.  Given TCP is not
   appropriate for deep space links[I-D.many-tiptop-usecase], another
   email forwarding solution has to be found using a transport protocol
   suited for deep space, such as a space profiled
   QUIC[I-D.many-tiptop-quic-profile].

   A more recent email protocol is JMAP [RFC8621] which uses REST over
   HTTP.  In deep space, JMAP could be run over HTTP3 over a space
   profiled QUIC.

   DNS insfrastructure need to be properly deployed and setup to avoid
   DNS requests through deep space links as discussed in
   [I-D.many-tiptop-dns].

3.  Deployment Recommendations

   Since TCP is not appropriate, HTTP over QUIC is used to transfer
   email over deep space.

   On Earth, current SMTP infrastructure is used.  For email to be
   forwarded from Earth to deep space, the following steps SHOULD be
   taken:

   *  an Earth mail gateway, as the last hop for email on Earth,
      receives email by SMTP

   *  the gateway converts the email to Batch SMTP (BSMTP) MIME object
      [RFC2442]

   *  the gateway sends the BSMTP object using HTTP3/QUIC to the
      corresponding gateway on the celestial body surface network

   *  the celestial body email gateway receives the BSMTP, disassemble
      it and then forwards it using SMTP to the final mail server on the
      celestial body network.

   Reversely, an email sent from a celestial body surface network to
   Earth SHOULD follow these steps:

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   *  email is forwarded to the SMTP gateway on that network

   *  The SMTP gateway converts the email to Batch SMTP MIME object
      [RFC2442]

   *  The gateway sends it using HTTP3/QUIC to the corresponding gateway
      on Earth.

   The Earth HTTP endpoint may be statically configured on the celestial
   body gateway.

4.  Discovering the Next Mail Server

   Given the low number of celestial body networks, the use of DNS
   lookup may be avoided by having a static map of destination domains
   to HTTP endpoints, configured on the Earth mail gateway.

   Given the use of HTTP which requires specifying a full URI, the DNS
   MX resource record (RR) only provides the hostname of the mail
   server, not the full URI.

   The DNS URI resource record[RFC7553] SHOULD be used instead of MX
   rRR.  The URI RR provides similar facility of the MX or SRV records
   enabling specifying multiple equivalent mail servers with weights, as
   well as multiple servers with different priorities.  The service name
   used in the query should be "_bsmtp._https".  As discussed in
   Section 8, the "bsmtp" service name is registered in IANA service
   names registry.

   For example, the last email hop on Earth receiving an SMTP message to
   be forwarded to user1@moon.spaceagency.int have to find the URI and
   IP address of the email server on Moon.  It queries the DNS for the
   URI RR of "_bsmtp._http.moon.spaceagency.in".  The DNS response is as
   follows:

   *  _bsmtp._https IN URI 10 1
      "https://moonmailgateway1.spaceagency.int/inboundmail"

   *  _bsmtp._https IN URI 20 1
      "https://moonmailgateway2.spaceagency.int/inboundmail"

   The URI RRs received above indicate with the highest priority, noted
   with the lowest priority number (10 instead of 20) that the host
   moonmailgateway1.spaceagency.int should be contacted first for email
   delivery and if not available, then the next priority will be used
   (moonmailgateway2.spaceagency.int).  The Earth email server will then
   query the DNS for IP address records (A and AAAA) of
   moonmailgateway1.spaceagency.int.  When received, it will connect

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   moonmailgateway1.spaceagency.int using HTTP3 over QUIC at the full
   URI received previously "https://moonmailgateway1.spaceagency.int/
   inboundmail".

5.  Transport Considerations

   As noted in [I-D.many-tiptop-ip-architecture], the transport of BSMTP
   email over HTTP on deep space links should be accomplished over QUIC
   with proper transport configuration, as specified in
   [I-D.many-tiptop-quic-profile].

6.  DNS Considerations

   For emails sent from Earth, if the DNS is used, the looked up URI
   records and their corresponding IP address records should point to
   the gateway on the target celestial body network.  Those records
   should be located or cached on the DNS infrastructure on Earth.

   Similarly, if the DNS is used on the celestial body network, it is
   assumed that there will be a local DNS infrastructure that has a
   cache of the related records, as discussed in [I-D.many-tiptop-dns].

   Mail headers such as Received and others contain domain names of the
   whole email path, which may contain various hosts on Internet.
   Lookup of those names on the celestial body network SHOULD NOT be
   done as the local cache cannot contain all the possible mail server
   names on Internet.

7.  Unwanted Email Considerations

   To minimize use of scarce deep space bandwidth, strong anti-spamming
   should be done before leaving Earth.

   An anti-spamming system on the celestial body network should not rely
   on any database or DNS lookup located on Earth.

8.  IANA Considerations

   By this specification, the "bsmtp" service name, referring to
   [RFC2442] BSMTP specification, is registered as a service name under
   RFC6335 policy.

9.  Security Considerations

   TBD

10.  References

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10.1.  Normative References

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119,
              DOI 10.17487/RFC2119, March 1997,
              <https://www.rfc-editor.org/info/rfc2119>.

   [RFC8174]  Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
              2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
              May 2017, <https://www.rfc-editor.org/info/rfc8174>.

   [RFC2442]  Freed, N., Newman, D., Belissent, J., and M. Hoy, "The
              Batch SMTP Media Type", RFC 2442, DOI 10.17487/RFC2442,
              November 1998, <https://www.rfc-editor.org/info/rfc2442>.

   [RFC7553]  Faltstrom, P. and O. Kolkman, "The Uniform Resource
              Identifier (URI) DNS Resource Record", RFC 7553,
              DOI 10.17487/RFC7553, June 2015,
              <https://www.rfc-editor.org/info/rfc7553>.

10.2.  Informative References

   [RFC8621]  Jenkins, N. and C. Newman, "The JSON Meta Application
              Protocol (JMAP) for Mail", RFC 8621, DOI 10.17487/RFC8621,
              August 2019, <https://www.rfc-editor.org/info/rfc8621>.

   [I-D.many-tiptop-usecase]
              Blanchet, M., Eddy, W., and M. Eubanks, "IP in Deep Space:
              Key Characteristics, Use Cases and Requirements", Work in
              Progress, Internet-Draft, draft-many-tiptop-usecase-03, 18
              June 2025, <https://datatracker.ietf.org/doc/html/draft-
              many-tiptop-usecase-03>.

   [I-D.many-tiptop-ip-architecture]
              Blanchet, M., Eddy, W., and T. Li, "An Architecture for IP
              in Deep Space", Work in Progress, Internet-Draft, draft-
              many-tiptop-ip-architecture-01, 7 July 2025,
              <https://datatracker.ietf.org/doc/html/draft-many-tiptop-
              ip-architecture-01>.

   [I-D.many-tiptop-dns]
              Blanchet, M., "Deployment and Use of the Domain Name
              System(DNS) in Deep Space", Work in Progress, Internet-
              Draft, draft-many-tiptop-dns-00, 1 July 2025,
              <https://datatracker.ietf.org/doc/html/draft-many-tiptop-
              dns-00>.

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   [I-D.many-tiptop-quic-profile]
              Blanchet, M., "QUIC Profile for Deep Space", Work in
              Progress, Internet-Draft, draft-many-tiptop-quic-profile-
              00, 19 February 2025,
              <https://datatracker.ietf.org/doc/html/draft-many-tiptop-
              quic-profile-00>.

Acknowledgements

   Initial discussions on this subject were with John Levine who helped
   a lot in ironing out many aspects and Pete Resnick.

Author's Address

   Marc Blanchet
   Viagenie
   Canada
   Email: marc.blanchet@viagenie.ca

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