Internet-Draft       The "Pc" field for SMTP            Gururaja Grandhi
                                                 Hewlett-Packard Company
Expires: November 03, 2005                                  May 03, 2005


                       The "Pc" field for SMTP
                     draft-grandhi-pc-smtp-00.txt

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Copyright Notice

      Copyright (C) The Internet Society (2004).  All Rights Reserved.

Abstract

    This draft specifies a mechanism by which an SMTP sender can send
    a copy of mail to multiple recipients, with out exposing other's
    mail address to recipient and vice versa.

1.  Introduction

   Currently if a sender wants to send a message to multiple addresses
   without exposing the other's mail address, then the sender uses the
   "Bcc" field in the Mail header to hide the identities marked in the
   "Bcc" field. The recipients of the mail marked under "Bcc" list will
   not either have his mail address in the "To" or "Cc" list. Sometimes
   there is a high chance that this mail gets ignored by the recipient
   as he is not addressed directly and it is just a blind carbon copy.
   This draft specifies a mechanism through which a sender can send a
   copy of message to multiple recipients with a special field in the
   Mail header, which would interpreted by the SMTP server as "To" list,
   however protecting their identities from others in the mail
   communication (something like members in Bcc field and without
   affecting the other fields in the mail header).

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2. Conventions Used in this Document

   The key words "REQUIRED", "MUST", "MUST NOT", "SHOULD", "SHOULD
   NOT", and "MAY" in this document are to be interpreted as described
   in "Key words for use in RFCs to Indicate Requirement Levels"
   [KEYWORDS].

3. Requirement

   The requirement is to provide the user a new field "Pc", that
   achieves the similar functionality as that of a "Bcc" field.
   However, the "Pc" recipients of this message will be treated as
   primary recipients.

4. Header Updates

   A new field needs to be added into the SMTP header [RECEIVER FIELDS]
   called "Pc". The SMTP server would ensure to use a member of the "Pc"
   list as "To" list while delivering to SMTP receiver, however
   protecting his/her identity to others and vice versa. 
   The intermediate MTAs which does not support "Pc" field will
   ignore the "Pc" field, which MAY cause the "Pc" field recipient
   not receiving the mail.

5. Format of the Field

   The format specification of this field should be treated as
   a "Cc" field. This field would be a part of the header and
   would be carried forward throughout the mail thread.

6.  Processing of the "Pc" Field

   Client: The client must treat the "Pc" field as similar to "Cc"
   field while sending the mail to SMTP servers. The "Pc" list should
   be added in the Mail header before sending the mail.

   Server: The "Pc" field MUST be processed only at the final receiver's
   SMTP servers. Before storing the received message in the message
   store,  for each of the users in the Pc field, the corresponding
   mail address MUST be appended to the "To:" list of the message.
   The remaining mail addresses in the "Pc" list SHOULD be ignored. All
   the remaining fields like To,Cc,Bcc SHOULD be the same in the mail.
   The "Pc" field MUST be processed after the alias [ALIAS] has been
   expanded. If an alias is in the "Pc" list, all the members of the 
   alias [ALIAS] should get the ALIAS name in the "To:" list. 

   Relay/Gateway: The Relay/Gateway SHOULD just forward the "Pc" 
   field as it is to the next Relay/Gateway.

7. Formal Syntax
   
    The following syntax specification uses the Augmented Backus-Naur
    Form (ABNF) notation as specified in [ABNF]. This syntax reuses the 
    appropriate formal syntax defined in the INTERNET MESSAGE FORMAT   

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   Pc              = "Pc:" address-list CRLF

   CRLF            =  Carriage return (CR, ASCII value 13) and
                      Line feed (LF, ASCII value 10)
                       
   address-list    =  (address *("," address)) / obs-addr-list

   address         =  mailbox / group
  
   mailbox         =  name-addr / addr-spec

   name-addr       =  [display-name] angle-addr

   angle-addr      =  [CFWS] "<" addr-spec ">" [CFWS] / obs-angle-addr
   
   CFWS            =  *([FWS] comment) (([FWS] comment) / FWS)

   FWS             =  ([*WSP CRLF] 1*WSP) /   ; Folding white space
                        obs-FWS

   obs-FWS         =  1*WSP *(CRLF 1*WSP)

   ctext           =  NO-WS-CTL /     ; Non white space controls
                      %d33-39 /       ; The rest of the US-ASCII
                      %d42-91 /       ;  characters not including "(",
                      %d93-126        ;  ")", or "\"

   ccontent        =  ctext / quoted-pair / comment

   comment         =  "(" *([FWS] ccontent) [FWS] ")"

   addr-spec       =  local-part "@" domain

   local-part      =  dot-atom / quoted-string / obs-local-part

   domain          =  dot-atom / domain-literal / obs-domain

   domain-literal  =  [CFWS] "[" *([FWS] dcontent) [FWS] "]" [CFWS]

   dcontent        =  dtext / quoted-pair

   dtext           =  NO-WS-CTL /     ; Non white space controls

                      %d33-90 /       ; The rest of the US-ASCII
                      %d94-126        ;  characters not including "[",
                                        ;  "]", or "\"


   group           =  display-name ":" [mailbox-list / CFWS] ";"
                      [CFWS]

   mailbox-list    =  (mailbox *("," mailbox)) / obs-mbox-list


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   address-list    =  (address *("," address)) / obs-addr-list

   
   obs-addr-list   =  1*([address] [CFWS] "," [CFWS]) [address] 
                      (([FWS] comment) / FWS) 

   CFWS            =  *([FWS] comment) (([FWS] comment) / FWS)

   FWS             =  ([*WSP CRLF] 1*WSP) /   ; Folding white space
                      obs-FWS

   WSP             =  space (SP,ASCII value 32) and horizontal tab 
                      (HTAB, ASCII value 9) characters
                    
   obs-FWS         =   1*WSP *(CRLF 1*WSP)


8. Reply Mail headers

   The reply mail header will be similar to the recipient who had 
   received mail through "Bcc" field.

9. Security Consideration

   The intermediate MTAs which does not support "Pc" field will
   ignore the "Pc" field, which MAY cause the "Pc" field recipient
   not receiving the mail.

   There will not be any impact on Spam filters with this new field
   addition because, for an recipient, "Pc" field is equivalent to
   "To" and existing filters should work as it is.

10. Example

   A wants to send a mail to the people B,C,D with out any of them
   knowing about the other mail addresses.
  
   From: A 
   To: X
   Pc: B,C,D
   CC: Y
   Subject: TEST            


   Recipient X's mail looks like:
   From: A
   To:  X
   CC: Y
   Subject: TEST

   SMTP server capable of delivering the mail to B will append the
   mails "To" list with B.



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   Recipient B's mail looks like:

   From: A
   To:  X,B
   CC: Y
   Subject: TEST


   Recipient C's mail looks like:

   From: A
   To:  X,C
   CC: Y
   Subject: TEST

   Recipient D's mail looks like:

   From: A
   To:  X,D
   CC: Y
   Subject: TEST

   Recipient Y's mail looks like:

   From: A
   To:  X
   CC: Y
   Subject: TEST

Appendices

A. References

  The following documents contain definitions or specifications that
  are necessary to understand this document properly:

   
   [ALIAS]                    J. Klensin, "Simple Mail Transfer 
                              Protocol", RFC: 2821, April 2001.
      
   [RECEIVER FIELDS]          Crocker, D., "Standard of the Format of 
                              ARPA Internet Text Messages", RFC 822, 
                              August 1982.  
   
   [KEYWORDS]                 Bradner, S., "Key words for use in
                              RFCs to Indicate Requirement Levels",
                              BCP 14, RFC 2119, March 1997.

   [INTERNET MESSAGE FORMAT]  P. Resnick, "Internet Message Format",
                              RFC 2822, April 2001.

   [ABNF]                     Crocker, D. and P. Overell, "Augmented
                              BNF for Syntax Specifications: ABNF",
                              RFC 2234, November 1997.

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Author's Address

  Gururaja Grandhi
  Hewlett-Packard,
  29, Cunningham road,
  Bangalore,
  India 560052
  gururaja.grandhi@hp.com
  +91-80-2205-2884


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