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INTERNET-DRAFT                                                 W. Storey
<draft-storey-smtp-client-id-07.txt>                          LinuxMagic
Intended Status: Standards Track
Expires December 6, 2019                                    June 6, 2019

               SMTP Service Extension for Client Identity
                  <draft-storey-smtp-client-id-07.txt>

Abstract

   This document defines an extension for the Simple Mail Transfer
   Protocol (SMTP) called "CLIENTID" to provide a method for clients to
   indicate an identity to the server.

   This identity is an additional token that may be used for security
   and/or informational purposes, and with it a server may optionally
   apply heuristics using this token.

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), its areas,
   and its working groups.  Note that other groups may also distribute
   working documents as Internet-Drafts.

   Internet-Drafts are draft documents valid for a maximum of six months
   and may be updated, replaced, or obsoleted by other documents at any
   time.  It is inappropriate to use Internet-Drafts as reference
   material or to cite them other than as "work in progress."

   The list of current Internet-Drafts can be accessed at
   http://www.ietf.org/1id-abstracts.html

   The list of Internet-Draft Shadow Directories can be accessed at
   http://www.ietf.org/shadow.html

Copyright Notice

   Copyright (c) 2016 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

   This document is subject to BCP 78 and the IETF Trust's Legal
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   (http://trustee.ietf.org/license-info) in effect on the date of
   publication of this document.  Please review these documents
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   to this document.  Code Components extracted from this document must



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   include Simplified BSD License text as described in Section 4.e of
   the Trust Legal Provisions and are provided without warranty as
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Table of Contents

   1.  Introduction .................................................  3
   2.  The CLIENTID Service Extension ...............................  4
   3.  The CLIENTID Keyword of the EHLO Command .....................  4
   4.  The CLIENTID Command .........................................  5
   5.  Formal Syntax ................................................  5
   6.  Discussion ...................................................  6
       6.1. Applying heuristics to CLIENTID .........................  6
       6.2. Utility of CLIENTID .....................................  6
       6.3. Use Cases of CLIENTID ...................................  7
       6.4. Other SMTP Client Identifiers ...........................  9
       6.5. Future Considerations ...................................  9
   7.  Client Identity Types ........................................  9
   8.  Examples ..................................................... 11
       8.1 UUID Address as Client Identity .......................... 11
       8.2 Client Identity Without a TLS/SSL Session ................ 12
       8.3 Client Identity Leading to Rejection ..................... 12
       8.4 Malformed CLIENTID Command ............................... 13
   9.  Security Considerations ...................................... 13
   10. IANA Considerations .......................................... 14
       10.1 SMTP Extension Registration ............................. 14
   11. References ................................................... 14
       11.1 Normative References .................................... 14

1. Introduction

   The [SMTP] protocol and its extensions describe methods whereby an
   SMTP client may provide identity and/or authentication information to
   an SMTP server.  However, these existing methods are subject to
   limitations and none offer a way to identify the SMTP client with
   absolute confidence.  This document defines an SMTP service extension
   to provide an additional identity token which can represent the SMTP
   client with a higher degree of certainty when accessing the SMTP
   server.

   Typically SMTP clients are identified by establishing an authorized
   connection using the [AUTH] SMTP extension.  SMTP servers are often
   subject to malicious clients attempting to use authorized identities
   not intended for their use (often referred to as a brute-force
   attack).  When such an attack is attempted, the SMTP server may be
   unable to identify the impersonation and restrict such an unintended
   use by someone other than the authorized user of said credentials.
   While there are ways to identify the source of the SMTP client such
   as its IP address or EHLO identity, it would be useful if there was
   an additional way to uniquely identify the client in a method solely
   available across an encrypted channel.

   Using the CLIENTID extension, an SMTP client can provide an
   additional identity token to the server called its "client identity".
   The client identity can provide unique characteristics about the
   client accessing the SMTP service and may be combined with existing
   identification mechanisms in order to identify the client.  An SMTP

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   server may then apply additional security policies using this
   identity such as restricting use of the service to clients presenting
   recognized client identities, or only allowing use of authorized
   identities that match previously established client identities.

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
   document are to be interpreted as described in [KEYWORDS].

2. The CLIENTID Service Extension

   The following SMTP service extension is hereby defined:

   1. The name of this [SMTP] service extension is "Client Identity".

   2. The EHLO keyword value associated with this extension is
      "CLIENTID".

   3. The CLIENTID keyword has no parameters.

   4. A new [SMTP] verb "CLIENTID" is defined.

   5. No parameter is added to any SMTP command.

   6. This extension is appropriate for the submission protocol
      [SUBMIT].

3. The CLIENTID Keyword of the EHLO Command

   The CLIENTID keyword is used to tell the SMTP client that the SMTP
   server supports the CLIENTID service extension. Though certain
   conditions must be met before the CLIENTID keyword can be advertised.

   1. An SMTP server MUST NOT advertise the CLIENTID keyword in any EHLO
      responses if the CLIENTID extension support is not enabled.

   2. An SMTP server MUST NOT advertise the CLIENTID keyword in any EHLO
      response if the connection is not encrypted.

   3. An SMTP server MUST advertise the CLIENTID keyword in all EHLO
      responses after the connection is successfully encrypted (if
      CLIENTID is supported).

4. The CLIENTID Command

   The format for the CLIENTID command is:

   CLIENTID client-id-type client-id-token

      Arguments:

          client-id-type: A string identifying the identity type the
          client is providing.  It MUST be between 1 and 16 characters
          and comprised of only alphanumeric and dash characters.

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          client-id-token: A string identifying the client.  It MUST
          be between 1 and 128 printable characters.

      Restrictions:

          An SMTP client MUST NOT issue a CLIENTID command unless a
          TLS/SSL session has been negotiated as described in [STARTTLS]
          or through other means such as over a historical SMTP-SSL
          connection.  An SMTP server MUST reject any CLIENTID command
          sent before establishing an encrypted connection with a 500
          reply.

          An SMTP client MUST only issue the CLIENTID command after the
          SMTP server advertises the CLIENTID keyword via an EHLO
          command.  An SMTP server MUST reject a CLIENTID command prior
          to advertsing the CLIENTID keyword via an EHLO command.

          An SMTP server MUST reject any CLIENTID command that is not
          well formatted with a 501 reply.

          An SMTP client MUST NOT issue any subsequent CLIENTID commands
          after a successful CLIENTID command in the same session.  An
          SMTP server MUST reject any subsequent CLIENTID commands after
          a successful CLIENTID command in the same session with a 503
          reply.

          An SMTP client MUST issue any CLIENTID commands prior to
          issuing an [AUTH] command. An SMTP server MUST reject any
          CLIENTID command after receiving an [AUTH] command with a 503
          reply.

          Several SMTP service extensions such as [AUTH] require that an
          SMTP session be reset to an initial state under conditions
          such as after applying a security layer.  An SMTP server MUST
          discard any CLIENTID information after such a reset.

5. Formal Syntax

   The following syntax specification uses the Augmented Backus-Naur
   Form notation as specified in [ABNF].  Non-terminals referenced but
   not defined below are as defined by [ABNF].

   Except as noted otherwise, all alphabetic characters are case-
   insensitive.

      client-id-type-char = ALPHA / DIGIT / "-"
                          ;; alphanumeric and dash character

      client-id-type      = 1*16 client-id-type-char

      client-id-token     = 1*128 VCHAR
                          ;; any printable US-ASCII character



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6. Discussion

6.1 Applying heuristics to CLIENTID

   This section discusses the possible heuristics that can be applied to
   the information that is presented via the CLIENTID command.  This
   information includes whether a valid CLIENTID command was issued, the
   client identity type and the client identity token.

   1. An SMTP server MAY choose to require that a successful CLIENTID
      command be issued, or that a particular client type be presented
      before processing or accpeting an authentication request.

   2. An SMTP server MAY reject any authentication request not preceded
      with a client identity type that matches ACL's or rules as defined
      in the SMTP server.

   3. An SMTP server MAY reject any authentication request preceded by a
      CLIENTID command that contains a client identity type or client
      identity token that the server chooses not to accept for any
      reason such as by policy.

   4. An SMTP server MAY reject any authentication request preceded by a
      CLIENTID command that contains a client identity type or client
      identity token that the server has chosen to disable or revoke use
      of either temporarily or permanently.

   5. An SMTP server MAY reject any authentication request where the
      provided client identity is not on the list of permitted clients
      for the account holder.

   The SMTP server SHOULD only ever reject an SMTP client based on
   CLIENTID information during or after the authentication
   process/handler.  In the interest of limiting the amount of
   information being revealed, the rejection message SHOULD be as
   generic as possible and SHOULD NOT reveal any information on the
   heuristics or rules on which it bases it's decisions.

   Even if the client identity type and/or client identity token are not
   recognized, supported or permitted by the server and/or the owner of
   the authentication credentials, the presented information may still
   be useful for analysis.

6.2 Utility of CLIENTID

   Regardless of how frowned upon, users commonly reuse authorization
   information (like the username and password pair) across multiple
   services.  When one service is compromised, malicious actors can also
   gain access to other services where the user also used the same
   credentials.  Based on this representative problem alone, the utility
   of CLIENTID as an additional layer of determining the rights to
   present such authorization information becomes quickly apparent.

   The utility of CLIENTID may be seen by considering the following:

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   1. An SMTP client may be present on a device that does not have a
      useful domain name or network address, such as a mobile
      device, so its EHLO identity may be ambiguous.

   2. An SMTP client may utilize the same SMTP server with multiple
      different authorized identities, so an identity that persists
      across authorized identities is lacking.

   3. An authorized identity may make use of multiple discrete
      devices over different SMTP sessions, so an identity
      persisting on one device is lacking.

   4. The SMTP DATA payload does not need to be inspected for this
      identity.

   5. Connection information, a type of identity, such as network
      address frequently changes.

   However, this extends beyond just the restriction of authentication.
   While it might be argued that this can be served as a special form of
   SASL, by implementing this in the SMTP service itself, the SMTP
   service can choose before allowing a connection to be passed to a
   SASL implementation, allowing it to perform other heuristics, such as
   identifying brute force attacks more effeciently.

   The recent evolution of the internet as a whole has brought about
   large scale data breaches, compromised botnets comprising of millions
   of nodes, the transition to Carrier Grade NAT and the flourishing of
   IoT devices means traditional methods of protecting against brute
   force attacks have become much more difficult.  Traditional methods
   such as rate limiting and/or blocking access by IP are no longer
   viable without introducing collateral effects, such as either
   blocking legitimate user, or creating the conditions that allow DOS
   (Denial of Service) to legitimate users.

   Historically, SMTP and other services used what is technically a two
   factor, the email/user and password, albeit not effective in that the
   email is a KNOWN value.  And with the propensity for users to use a
   simple password, and the hundreds of millions of email addresses
   exposed in data breaches, or available by other means the ability to
   brute force is quite simple. While of course it is recommended that
   users use longer and more secure passwords, this is not the de facto
   situation, and the threats when credentials get compromised are
   significant.  And with 'botnet' operators able to engage millions of
   IoT in a distributed brute force, the status quo is in danger. Adding
   another non-public factor to be used as part of access control adds
   a strength against brute force by many factors and accomplishes it in
   a backwards compatible fashion, encouraging adoption.

   Under brute force attacks, rate limiting or blocking by IP Address
   was possible with little damage.  But with the proliferaction of IoT
   devices, smart phones, and the run-out of IP space, we have
   conditions where thousands of devices could be behind an IP Address,
   or IP(s) that are dynamic with devices changing IP(s) in minutes,

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   blocking or rate limiting an IP bears risks of blocking legitimate
   users.  By implementing a level of uniqueness to a connecting device,
   it introduces the ability to restrict or block a subset from
   connecting to the service for either brute force or dictionary
   attacks, while still allowing other devices to continue to be able to
   present authentication successfully.

   While 'forgery' and/or the use of random client identifier is
   possible, such behavior is also more readily detectable when a device
   identifier is presented.

   1. The SMTP server, when faced with hundreds of devices behind the
      same IP address, during an attack can restrict authentication
      attempts to only connections presenting a valid client identifier
      token.

   2. The SMTP server, during an attack, can restrict authentication to
      only historically known devices.

   3. The SMTP server can differentiate between many different devices
      behind the same IP, and apply maximum connections per device,
      rather than maximum connections per IP.

   4. While a person may present authentication credentials from many
      different geographical locations, eg, home, office, and travel, a
      single device will not in general be able to be in two
      geographical locations at the same time.  The SMTP server will
      have new information to apply to threat detection heuristics, ie
      to treat the use of the same client identifier token from two
      locations, as a possible brute force or forgery situation.

6.3 Use Cases of CLIENTID

   The SMTP server may use the additional information from CLIENTID with
   its interactions with SMTP clients in the following manner:

   1. Restrict use of an authorized identity to a set of client
      identities, thereby offering an added level of security.  For
      example, the use of an authorized identity may only be permitted
      from a single device using the client identity as a form of
      whitelisting.

   2. Identify that the same client identity is used to access multiple
      authorized identities and restrict access to the SMTP service.
      For example, a client that has successfully gained access to many
      authorized identities may be identified through its use of a
      shared client identity.

   3. Retain knowledge of client identities previously presented with an
      authorized identity and if an identity not previously seen is used
      restrict access to the SMTP service.

   4. Require that the SMTP client present a token such as a license key
      established outside of the SMTP session in order to make use of

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      any authorized identity;

   5. Apply different security policies to clients that provide a client
      identity versus those which do not.  For example, provide clients
      providing such an identity with additional trust.

   6. Ability to rate limit or block based on the presented client
      identifier token when multiple devices use a shared IP address
      without affecting other devices.

   7. Ability to detect distributed and localized dictionary attacks
      and brute force attacks.

   8. Use the client identifier token as a third factor to be passed
      to authentication methods. [SASL]

6.4. Other SMTP Client Identifiers

   The [SMTP] protocol and its extensions describe methods whereby an
   SMTP client may provide identity information to an SMTP server.  Some
   of these identities are listed for contrast:

   1. The client connection source provides an IP address associated
      with the SMTP session. This may be accompanied by a PTR record
      and/or GeoIP information.

   2. The EHLO command allows a client to identify itself with a domain
      or address for an SMTP session.

   3. The [AUTH] SMTP extension allows the client to establish an
      authorized identity for an SMTP session.

   4. The MAIL command identifies a specific sender for a mail
      transaction.

6.5. Future Considerations

   In the future there may be a demand for being able to provide
   multiple CLIENTID commands with different client identity types.
   For instance, it may be desirable for a device to identify itself,
   both with a hardware device identifier and a software identifier.
   We believe this to be out of scope, and can be accomodated with a
   special client identifier token which encapsulates both.

7. Client Identity Types

   This document does not specify any CLIENTID identity type that MUST
   be supported.  The client identity type is meant to be defined by
   the client implementation that is designed to access the SMTP server
   and protocol. For instance, many SMTP client software implementations
   already create a distinct UUID for each account.  Some commercial
   email clients have a license key. Some physical devices that need to
   of client identity type that conforms to the definition, it is
   interact with SMTP might have a unique hardware ID or MAC Address.

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   While there is no pre-defined list of client identity type defined by
   this RFC, and all SMTP servers should be prepared to accept any form
   suggested that SMTP client developers carefully consider the name of
   the client identity type.  For example, rather that using a
   client identity type of UUID, consider the advantages of making it
   more distinct, eg "<product_short_code>UUID".  This way the SMTP
   server can better record histories, eg the difference between say
   a Thunderbird generated unique id, and a Mutt generated unique id.

   Some examples of identity type might be UUID, LICENSE,
   DEVICE_ID, MAC and/or COOKIE.  It is expected that the most common
   types might be related to distinct UUID, LICENSEKEY, or HARDWAREID.

   An SMTP server SHOULD NOT reject an unidentified CLIENTID type,
   except for specific policy use cases.

   It is envisioned that in the future it will be useful to propose
   a set of standardized client-identity-type to help with validation,
   or to allow the SMTP server to apply ACL rules on expected types,
   this would be an extension to this RFC.

   1. UUID

      UUID is a common practice to represent either a individual user,
      hardware device or software installation associated with a
      specific individual. The support of UUID enables existing UUID
      implementations to be used to semi-uniquely identify a device
      associated with an individual. A definition of the format should
      be considered. Otherwise non-standard UUID might be a separate
      type specific to the software implementation, for instance
      TBIRD-UUID.

   2. LICENSE

      An SMTP client may find it useful to identify the license key of
      software it is using.  Such licenses are typically crafted such
      that they are unique and useful to identify a software
      installation.  This is more normally suited for a software
      designed for a single-user.  While LICENSE could be standard type
      again, it might more more helpful to specify a vendor specific
      type such as BBLICENSEKEY.

   3. DEVICE_ID

      Many hardware devices are designed to be used by a single
      individual and already have an associated hardware device id.
      While a standard type might be defined, it also might be more
      helpful to use a vendor specific type, such as ATOM-DEVICEID.

   4. MAC

      The MAC address traditionally was used as a worldwide identifier
      both of the unique device, as well as it's vendor and product
      category, however this is not always the case anymore, in the case

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      of it's usage in 'virtual' devices.  But for many hardware devices
      which are required to access a defined SMTP resource, the MAC
      address may still be a simple unique identifier.  MAC should NOT
      be used, unless this is a MAC address that can be associated to a
      vendor using standard MAC registration information as defined or
      set by the IEEE Standards Association and is meant to represent a
      unique device.

   5. COOKIE

      While not guranteed to be consistent many web applications are
      designed to access SMTP directly and may need to have a
      semi-unique identifier available as part of the web based
      transaction.  It is assumed that COOKIE encompasses the group of
      web based tokens known to persist from session to session. A
      specific web based application can provide sufficient information
      in the actual client-identifier-token to differentiate between
      applications and or websites, and are convenient as they can be
      related to very specific domains, and are universally available to
      web application designers.

   As a reminder, an SMTP server SHOULD NOT retain and/or store the
   CLIENTID information WITH authentication credentials or
   authentication systems directly, but the SMTP service MAY
   associate the CLIENTID with a specific account holder, eg to create
   a history file of known CLIENTID tokens associated or permitted to
   access or present authentication credentials for that account holder.

   This document recommends that a server associates a set of flags that
   describes how the CLIENTID command should be handled for any given
   client identity type.

   1. Handled but treat as not presented (ignored, no persistance)
   2. Store in SMTP session but treat as not presented (for debugging)
   3. Store in the SMTP session, so it is available to System log
   4. Store in the SMTP session, so it is available to User log
   5. Use for authentication
   6. Use for alert when authentication fails
   7. Use for alert when authentication succeeds
   8. Unused

8. Examples

8.1 UUID Address as Client Identity

   C: [connection established]
   S: 220 server.example.com ESMTP ready
   C: EHLO client.example.net
   S: 250-server.example.com
   S: 250-STARTTLS
   S: 250 AUTH LOGIN
   C: STARTTLS
   S: 220 Go ahead
   C: <starts TLS negotiation>

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   C & S: <negotiate a TLS session>
   C & S: <check result of negotiation>
   C: EHLO client.example.net
   S: 250-server.example.com
   S: 250-AUTH LOGIN
   S: 250 CLIENTID
   C: CLIENTID UUID 23bf83be-aad7-46aa-9e0f-39191ccf402f
   S: 250 OK
   C: AUTH LOGIN dGVzdAB0ZXN0ADEyMzQ=
   S: 235 Authentication successful
   C: MAIL FROM:<sender@example.net>
   S: 250 OK
   C: RCPT TO:<receiver@example.com>
   S: 250 OK
   C: DATA
   S: 354 Ready for message content
   C: <body>
   C: .
   S: 250 OK
   C: QUIT
   S: 221 server.example.com Service closing transmission channel

8.2 Client Identity Without a TLS/SSL Session

   C: [connection established over a plaintext connection]
   S: 220 server.example.com ESMTP ready
   C: EHLO client.example.net
   S: 250-server.example.com
   S: 250 STARTTLS
   C: CLIENTID MAC 08:9e:01:70:f6:46
   S: 500 Syntax error, command unrecognised
   C: MAIL FROM:<sender@example.net>
   S: 250 OK
   C: QUIT
   S: 221 server.example.com Service closing transmission channel

   The server rejects use of the CLIENTID command as no TLS/SSL session
   was yet established.

8.3 Client Identity Leading to Rejection

   C: [connection established over a plaintext connection]
   S: 220 server.example.com ESMTP ready
   C: EHLO client.example.net
   S: 250-server.example.com
   S: 250 STARTTLS
   C: STARTTLS
   S: 220 Go ahead
   C: <starts TLS negotiation>
   C & S: <negotiate a TLS session>
   C & S: <check result of negotiation>
   C: EHLO client.example.net
   S: 250-server.example.com
   S: 250 CLIENTID

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   C: CLIENTID MAC 08:9e:01:70:f6:46
   S: 250 OK
   C: AUTH LOGIN dGVzdAB0ZXN0ADEyMzQ=
   S: 235 Authentication successful
   S: 550 Server policy does not permit your use of this mail system
   C: QUIT
   S: 221 server.example.com Service closing transmission channel

   The server rejects use of the mail system after deciding that the
   provided client identity does not establish sufficient privileges.

8.4 Malformed CLIENTID Command

   C: [connection established over a plaintext connection]
   S: 220 server.example.com ESMTP ready
   C: EHLO client.example.net
   S: 250-server.example.com
   S: 250 STARTTLS
   C: STARTTLS
   S: 220 Go ahead
   C: <starts TLS negotiation>
   C & S: <negotiate a TLS session>
   C & S: <check result of negotiation>
   C: EHLO client.example.net
   S: 250-server.example.com
   S: 250 CLIENTID
   C: CLIENTID MAC
   S: 501 Syntax error in parameters or arguments
   C: QUIT
   S: 221 server.example.com Service closing transmission channel

   The server rejects the CLIENTID command as it is not well formed due
   to there being only a single parameter provided.

9.  Security Considerations

   As this extension provides an additional means of communicating
   information from a client to a server it is clear there is additional
   information divulged to the server.  This may have privacy
   considerations depending on the client identity type or its contents.
   For example, it may reveal a MAC address of the device used to
   communicate with a server that would not previously have been
   revealed.  While it has been useful to use identifier such as email
   address for authentication it is easy for these authetication tokens
   to be shared and/or reused and/or be publically available for other
   purposes.  An SMTP server and or its operators SHOULD not share
   any CLIENTID information presented with a third party as it may
   represent or be linked to an individual and SHOULD never be shared in
   association with authentication tokens.

   As well, while this service extension requires that the identity
   information only be transmitted over an encrypted channel to reduce
   the risk of eavesdropping, it does not specify any policies or
   practices required in the establishment of such a channel, and so it

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   is the responsibility of the client and the server to determine that
   the communication medium meets their requirements.

10.  IANA Considerations

10.1 SMTP Extension Registration

   Section 2.2.2 of [SMTP] sets out the procedure for registering a new
   SMTP extension.

   This extension will need to be registered.

11.  References

11.1.  Normative References

   [ABNF]     Crocker, D., Ed., and P. Overell, "Augmented BNF for
              Syntax Specifications: ABNF", STD 68, RFC 5234, DOI
              10.17487/RFC5234, January 2008, <http://www.rfc-
              editor.org/info/rfc5234>.

   [AUTH]     Siemborski, R., Ed., and A. Melnikov, Ed., "SMTP Service
              Extension for Authentication", RFC 4954, DOI
              10.17487/RFC4954, July 2007, <http://www.rfc-
              editor.org/info/rfc4954>.

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

   [SMTP]     Klensin, J., "Simple Mail Transfer Protocol", RFC 5321,
              DOI 10.17487/RFC5321, October 2008, <http://www.rfc-
              editor.org/info/rfc5321>.

   [STARTTLS] Hoffman, P., "SMTP Service Extension for Secure SMTP over
              Transport Layer Security", RFC 3207, DOI 10.17487/RFC3207,
              February 2002, <http://www.rfc-editor.org/info/rfc3207>.

   [SUBMIT]   Gellens, R. and J. Klensin, "Message Submission for Mail",
              STD 72, RFC 6409, DOI 10.17487/RFC6409, November 2011,
              <http://www.rfc-editor.org/info/rfc6409>.

Contributors

   Michael Peddemors
   LinuxMagic

Authors' Addresses

   William Storey
   LinuxMagic
   #405 - 860 Homer St.
   Vancouver, British Columbia

Storey, William         Expires December 6, 2019               [Page 14]


INTERNET-DRAFT            SMTP Client Identity              June 6, 2019

   CA V6B 2W5

   EMail: william@linuxmagic.com

   Deion Yu
   LinuxMagic
   #405 - 860 Homer St.
   Vancouver, British Columbia
   CA V6B 2W5

   EMail: deiony@linuxmagic.com












































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