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RFC 2076 - Common Internet Message Headers

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Network Working Group                                          J. Palme
Request for Comments: 2076                     Stockholm University/KTH
Category: Informational                                   February 1997

                    Common Internet Message Headers

Status of this Memo

   This memo provides information for the Internet community.  This memo
   does not specify an Internet standard of any kind.  Distribution of
   this memo is unlimited.


   This memo contains a table of commonly occurring headers in headings
   of e-mail messages. The document compiles information from other RFCs
   such as RFC 822, RFC 1036, RFC 1123, RFC 1327, RFC 1496, RFC 1521,
   RFC 1766, RFC 1806, RFC 1864 and RFC 1911. A few commonly occurring
   headers which are not defined in RFCs are also included. For each
   header, the memo gives a short description and a reference to the RFC
   in which the header is defined.

Table of contents
   1. Introduction..............................................  2
   2. Use of gatewaying headers.................................  3
   3. Table of headers..........................................  3
        3.1 Phrases used in the tables..........................  3
        3.2 Trace information...................................  5
        3.3 Format and control information......................  5
        3.4 Sender and recipient indication.....................  6
        3.5 Response control....................................  9
        3.6 Message identification and referral headers......... 11
        3.7 Other textual headers............................... 12
        3.8 Headers containing dates and times.................. 13
        3.9 Quality information................................. 13
        3.10 Language information............................... 14
        3.11 Size information................................... 14
        3.12 Conversion control................................. 15
        3.13 Encoding information............................... 15
        3.14 Resent-headers..................................... 16
        3.15 Security and reliability........................... 16
        3.16 Miscellaneous...................................... 16
   4. Acknowledgments........................................... 18

   5. References................................................ 18
   6. Author's Address.......................................... 20
   Appendix A:
   Headers sorted by Internet RFC document in which they appear. 21
   Appendix B:
   Alphabetical index........................................... 25

1. Introduction

   Many different Internet standards and RFCs define headers which may
   occur on Internet Mail Messages and Usenet News Articles. The
   intention of this document is to list all such headers in one
   document as an aid to people developing message systems or interested
   in Internet Mail standards.

   The document contains all headers which the author has found in the
   following Internet standards: , RFC 822 [2], RFC 1036 [3], RFC 1123
   [5], RFC 1327 [7], RFC 1496 [8], RFC 1521 [11], RFC 1766 [12], RFC
   1806 [14], RFC 1864[17] and RFC 1911[20]. Note in particular that
   heading attributes defined in PEM (RFC 1421-1424) and MOSS (RFC 1848
   [16]) are not included. PEM and MOSS headers only appear inside the
   body of a message, and thus are not headers in the RFC 822 sense.
   Mail attributes in envelopes, i.e. attributes controlling the message
   transport mechanism between mail and news servers, are not included.
   This means that attributes from SMTP [1], UUCP [18] and NNTP [15] are
   mainly not covered either. Headings used only in HTTP [19] are not
   included yet, but may be included in future version of this memo. A
   few additional headers which often can be found in e-mail headings
   but are not part of any Internet standard are also included.

   For each header, the document gives a short description and a
   reference to the Internet standard or RFC, in which they are defined.

   The header names given here are spelled the same way as when they are
   actually used. This is usually American but sometimes English
   spelling.  One header in particular, "Organisation/Organization",
   occurs in e-mail headers sometimes with the English and other times
   with the American spelling.

   The following words are used in this memo with the meaning specified

   heading           Formatted text at the top of a message, ended by a
                     blank line

   header = heading  One field in the heading, beginning with a field
   field             name, colon, and followed by the field value(s)

   It is my intention to continue updating this document after its
   publication as an RFC. The latest version, which may be more up-to-
   date (but also less fully checked out) will be kept available for
   downloading from URL

   Please e-mail me (Jacob Palme <jpalme@dsv.su.se>) if you have noted
   headers which should be included in this memo but are not.

2. Use of gatewaying headers

   RFC 1327 defines a number of new headers in Internet mail, which are
   defined to map headers which X.400 has but which were previously not
   standardized in Internet mail. The fact that a header occurs in RFC
   1327 indicates that it is recommended for use in gatewaying messages
   between X.400 and Internet mail, but does not mean that the header is
   recommended for messages wholly within Internet mail. Some of these
   headers may eventually see widespread implementation and use in
   Internet mail, but at the time of this writing (1996) they are not
   widely implemented or used.

   Headers defined only in RFC 1036 for use in Usenet News sometimes
   appear in mail messages, either because the messages have been
   gatewayed from Usenet News to e-mail, or because the messages were
   written in combined clients supporting both e-mail and Usenet News in
   the same client. These headers are not standardized for use in
   Internet e-mail and should be handled with caution by e-mail agents.

3. Table of headers

3.1 Phrases used in the tables

   "not for general        Used to mark headers which are defined in RFC
   usage"                  1327 for use in messages from or to Internet
                           mail/X.400 gateways. These headers have not
                           been standardized for general usage in the
                           exchange of messages between Internet mail-
                           based systems.

   "not standardized       Used to mark headers defined only in RFC 1036
   for use in e-mail"      for use in Usenet News. These headers have no
                           standard meaning when appearing in e-mail,
                           some of them may even be used in different
                           ways by different software. When appearing in
                           e-mail, they should be handled with caution.
                           Note that RFC 1036, although generally used as
                           a de-facto standard for Usenet News, is not an
                           official IETF standard or even on the IETF
                           standards track.

   "non-standard"          This header is not specified in any of
                           referenced RFCs which define Internet
                           protocols, including Internet Standards, draft
                           standards or proposed standards. The header
                           appears here because it often appears in e-
                           mail or Usenet News. Usage of these headers is
                           not in general recommended. Some header
                           proposed in ongoing IETF standards development
                           work, but not yet accepted, are also marked in
                           this way.

   "discouraged"           This header, which is non-standard, is known
                           to create problems and should not be
                           generated. Handling of such headers in
                           incoming mail should be done with great

   "controversial"         The meaning and usage of this header is
                           controversial, i.e. different implementors
                           have chosen to implement the header in
                           different ways. Because of this, such headers
                           should be handled with caution and
                           understanding of the different possible

   "experimental"          This header is used for newly defined headers,
                           which are to be tried out before entering the
                           IETF standards track. These should only be
                           used if both communicating parties agree on
                           using them. In practice, some experimental
                           protocols become de-facto-standards before
                           they are made into IETF standards.

3.2 Trace information

   Used to convey the information       Return-Path:   RFC 821,
   from the MAIL FROM envelope                         RFC 1123: 5.2.13.
   attribute in final delivery, when
   the message leaves the SMTP
   environment in which "MAIL FROM"
   is used.

   Trace of MTAs which a message has    Received:      RFC 822: 4.3.2,
   passed.                                             RFC 1123: 5.2.8.

   List of MTAs passed.                 Path:          RFC 1036: 2.1.6,
                                                       only in Usenet
                                                       News, not in e-

   Trace of distribution lists          DL-Expansion-  RFC 1327, not for
   passed.                              History-       general usage.

3.3 Format and control information

   An indicator that this message is    MIME-Version:  RFC 1521: 3.
   formatted according to the MIME
   standard, and an indication of
   which version of MIME is

   Special Usenet News actions only.    Control:       RFC 1036: 2.1.6,
                                                       only in Usenet
                                                       News, not in e-

   Special Usenet News actions and a    Also-Control:  son-of-RFC1036
   normal article at the same time.                    [21], non-
                                                       standard, only in
                                                       Usenet News, not
                                                       in e-mail

   Which body part types occur in       Original-      RFC 1327, not for
   this message.                        Encoded-       general usage.

   Controls whether this message may    Alternate-     RFC 1327, not for
   be forwarded to alternate            Recipient:     general usage.
   recipients such as a postmaster
   if delivery is not possible to
   the intended recipient. Default:

   Whether recipients are to be told    Disclose-      RFC 1327, not for
   the names of other recipients of     Recipients:    general usage.
   the same message. This is
   primarily an X.400 facility. In
   X.400, this is an envelope
   attribute and refers to
   disclosure of the envelope
   recipient list. Disclosure of
   other recipients is in Internet
   mail done via the To:, cc: and
   bcc: headers.

   Whether a MIME body part is to be    Content-       RFC 1806,
   shown inline or is an attachment;    Disposition:   experimental
   can also indicate a suggested
   filename for use when saving an
   attachment to a file.

3.4 Sender and recipient indication

   Authors or persons taking            From:          RFC 822: 4.4.1,
   responsibility for the message.                     RFC 1123: 5.2.15-
                                                       16, 5.3.7,
   Note difference from the "From "                    RFC 1036 2.1.1
   header (not followed by ":")

   (1) This header should never         From           not standardized
   appear in e-mail being sent, and                    for use in e-mail
   should thus not appear in this
   memo. It is however included,
   since people often ask about it.

   This header is used in the so-
   called Unix mailbox format, also
   known as Berkely mailbox format
   or the MBOX format. This is a
   format for storing a set of
   messages in a file. A line
   beginning with "From " is used to
   separate successive messages in
   such files.

   This header will thus appear when
   you use a text editor to look at
   a file in the Unix mailbox
   format. Some mailers also use
   this format when printing
   messages on paper.

   The information in this header
   should NOT be used to find an
   address to which replies to a
   message are to be sent.

   (2) Used in Usenet News mail         From           RFC 976: 2.4 for
   transport, to indicate the path      or             use in Usenet News
   through which an article has gone    >From
   when transferred to a new host.

   Sometimes called "From_" header.

   Name of the moderator of the         Approved:      RFC 1036: 2.2.11,
   newsgroup to which this article                     not standardized
   is sent; necessary on an article                    for use in e-mail.
   sent to a moderated newsgroup to
   allow its distribution to the
   newsgroup members. Also used on
   certain control messages, which
   are only performed if they are
   marked as Approved.

   The person or agent submitting       Sender:        RFC 822: 4.4.2,
   the message to the network, if                      RFC 1123: 5.2.15-
   other than shown by the From:                       16, 5.3.7.

   Primary recipients.                  To:            RFC 822: 4.5.1,
                                                       RFC 1123: 5.2.15-
                                                       16, 5.3.7.

   Secondary, informational             cc:            RFC 822: 4.5.2,
   recipients. (cc = Carbon Copy)                      RFC 1123. 5.2.15-
                                                       16, 5.3.7.

   Recipients not to be disclosed to    bcc:           RFC 822: 4.5.3,
   other recipients. (bcc = Blind                      RFC 1123: 5.2.15-
   Carbon Copy).                                       16, 5.3.7.

   Primary recipients, who are          For-Handling:  Non-standard
   requested to handle the
   information in this message
   or its attachments.

   Primary recipients, who are          For-Comment:   Non-standard
   requested to comment on the
   information in this message
   or its attachments.

   In Usenet News: group(s) to which    Newsgroups:    RFC 1036: 2.1.3,
   this article was posted.                            not standardized
   Some systems provide this header                    and controversial
   also in e-mail although it is not                   for use in e-mail.
   standardized there.

   Unfortunately, the header can
   appear in e-mail with two
   different and contradictory

   (a) Indicating the newsgroup
   recipient of an article/message
   sent to both e-mail and Usenet
   News recipients.

   (b) In a personally addressed
   reply to an article in a news-
   group, indicating the newsgroup
   in which this discussion

   Inserted by Sendmail when there      Apparently-    Non-standard,
   is no "To:" recipient in the         To:            discouraged,
   original message, listing                           mentioned in
   recipients derived from the                         RFC 1211.
   envelope into the message
   heading. This behavior is not
   quite proper, MTAs should not
   modify headings (except inserting
   Received lines), and it can in
   some cases cause Bcc recipients
   to be wrongly divulged to non-Bcc

   Geographical or organizational       Distribution:  RFC 1036: 2.2.7,
   limitation on where this article                    not standardized
   can be distributed.                                 for use in e-mail.

   Fax number of the originator.        Fax:,          Non-standard.

   Phone number of the originator.      Phone:         Non-standard.

   Information about the client         Mail-System-   Non-standard.
   software of the originator.          Version:,
                                        Client:, X-
                                        Mailer, X-

3.5 Response control

   This header is meant to indicate     Reply-To:      RFC 822: 4.4.3,
   where the sender wants replies to                   RFC 1036: 2.2.1
   go. Unfortunately, this is                          controversial.
   ambiguous, since there are
   different kinds of replies, which
   the sender may wish to go to
   different addresses. In
   particular, there are personal
   replies intended for only one
   person, and group replies,
   intended for the whole group of
   people who read the replied-to
   message (often a mailing list,
   anewsgroup name cannot appear
   here because of different syntax,
   see "Followup-To" below.).

   Some mail systems use this header
   to indicate a better form of the
   e-mail address of the sender.
   Some mailing list expanders puts
   the name of the list in this
   header. These practices are
   controversial. The personal
   opinion of the author of this RFC
   is that this header should be
   avoided except in special cases,
   but this is a personal opinion
   not shared by all specialists in
   the area.

   Used in Usenet News to indicate      Followup-To:   RFC 1036: 2.2.3,
   that future discussions (=follow-                   not standardized
   up) on an article should go to a                    for use in e-mail.
   different set of newsgroups than
   the replied-to article. The most
   common usage is when an article
   is posted to several newsgroups,
   and further discussions is to
   take place in only one of them.

   In e-mail, this header may occur
   in a message which is sent to
   both e-mail and Usenet News, to
   show where follow-up in Usenet
   news is wanted. The header does
   not say anything about where
   follow-up in e-mail is to be

   Note that the value of this
   header must always be one or more
   newsgroup names, never e-mail

   Address to which notifications       Errors-To:,    Non-standard,
   are to be sent and a request to      Return-        discouraged.
   get delivery notifications.          Receipt-To:
   Internet standards recommend,
   however, the use of RCPT TO and
   Return-Path, not Errors-To, for
   where delivery notifications are
   to be sent.

   Whether non-delivery report is       Prevent-       RFC 1327, not for
   wanted at delivery error. Default    NonDelivery-   general usage.
   is to want such a report.            Report:

   Whether a delivery report is         Generate-      RFC 1327, not for
   wanted at successful delivery.       Delivery-      general usage.
   Default is not to generate such a    Report:

   Indicates whether the content of     Content-       RFC 1327, not for
   a message is to be returned with     Return:        general usage.
   non-delivery notifications.

   Possible future change of name       X400-Content-  non-standard
   for "Content-Return:"                Return:

3.6 Message identification and referral headers

   Unique ID of this message.           Message-ID:    RFC 822: 4.6.1
                                                       RFC 1036: 2.1.5.

   Unique ID of one body part of the    Content-ID:    RFC 1521: 6.1.
   content of a message.

   Base to be used for resolving        Content-Base:  Non-standard
   relative URIs within this content

   URI with which the content of        Content-       Non-standard
   this content part might be           Location:

   Reference to message which this      In-Reply-To:   RFC 822: 4.6.2.
   message is a reply to.

   In e-mail: reference to other        References:    RFC 822: 4.6.3
   related messages, in Usenet News:                   RFC 1036: 2.1.5.
   reference to replied-to-articles.

   References to other related          See-Also:      Son-of-RFC1036
   articles in Usenet News.                            [21], non-standard

   Reference to previous message        Obsoletes:     RFC 1327, not for
   being corrected and replaced.                       general usage.
   Compare to "Supersedes:" below.
   This field may in the future be
   replaced with "Supersedes:".

   Commonly used in Usenet News in      Supersedes:    son-of-RFC1036
   similar ways to the "Obsoletes"                     [21], non-standard
   header described above. In Usenet
   News, however, Supersedes causes
   a full deletion of the replaced
   article in the server, while
   "Supersedes" and "Obsoletes" in e-
   mail is implemented in the client
   and often does not remove the old
   version of the text.

   Only in Usenet News, similar to      Article-       son-of-RFC1036
   "Supersedes:" but does not cause     Updates:       [21], non-standard
   the referenced article to be
   physically deleted.

   Reference to specially important     Article-       son-of-RFC1036
   articles for a particular Usenet     Names:         [21], non-standard

3.7 Other textual headers

   Search keys for data base            Keywords:      RFC 822: 4.7.1
   retrieval.                                          RFC 1036: 2.2.9.

   Title, heading, subject. Often       Subject:       RFC 822: 4.7.1
   used as thread indicator for                        RFC 1036: 2.1.4.
   messages replying to or
   commenting on other messages.

   Comments on a message.               Comments:      RFC 822: 4.7.2.

   Description of a particular body     Content-       RFC 1521: 6.2.
   part of a message.                   Description:

   Organization to which the sender     Organization:  RFC 1036: 2.2.8,
   of this article belongs.                            not standardized
                                                       for use in e-mail.

   See Organization above.              Organisation:  Non-standard.

   Short text describing a longer       Summary:       RFC 1036: 2.2.10,
   article. Warning: Some mail                         not standardized
   systems will not display this                       for use in e-mail,
   text to the recipient. Because of                    discouraged.
   this, do not use this header for
   text which you want to ensure
   that the recipient gets.

   A text string which identifies       Content-       RFC 1327, not for
   the content of a message.            Identifier:    general usage.

3.8 Headers containing dates and times

   The time when a message was          Delivery-      RFC 1327, not for
   delivered to its recipient.          Date:          general usage.

   In Internet, the date when a         Date:          RFC 822: 5.1,
   message was written, in X.400,                      RFC 1123: 5.2.14
   the time a message was submitted.                   RFC 1036: 2.1.2.
   Some Internet mail systems also
   use the date when the message was

   A suggested expiration date. Can     Expires:       RFC 1036: 2.2.4,
   be used both to limit the time of                   not standardized
   an article which is not                             for use in e-mail.
   meaningful after a certain date,
   and to extend the storage of
   important articles.

   Time at which a message loses its    Expiry-Date:   RFC 1327, not for
   validity. This field may in the                     general usage.
   future be replaced by "Expires:".

   Latest time at which a reply is      Reply-By:      RFC 1327, not for
   requested (not demanded).                           general usage.

3.9 Quality information

   Can be "normal", "urgent" or "non-   Priority:      RFC 1327, not for
   urgent" and can influence                           general usage.
   transmission speed and delivery.

   Sometimes used as a priority         Precedence:    Non-standard,
   value which can influence                           controversial,
   transmission speed and delivery.                    discouraged.
   Common values are "bulk" and
   "first-class". Other uses is to
   control automatic replies and to
   control return-of-content
   facilities, and to stop mailing
   list loops.

   A hint from the originator to the    Importance:    RFC 1327 and
   recipients about how important a                    RFC 1911,
   message is. Values: High, normal                    experimental
   or low. Not used to control
   transmission speed.

   How sensitive it is to disclose      Sensitivity:   RFC 1327 and
   this message to other people than                   RFC 1911,
   the specified recipients. Values:                   experimental
   Personal, private, company
   confidential. The absence of this
   header in messages gatewayed from
   X.400 indicates that the message
   is not sensitive.

   Body parts are missing.              Incomplete-    RFC 1327, not for
                                        Copy:          general usage.

3.10 Language information

   Can include a code for the           Language:      RFC 1327, not for
   natural language used in a                          general usage.
   message, e.g. "en" for English.

   Can include a code for the           Content-       RFC 1766, proposed
   natural language used in a           Language:      standard.
   message, e.g. "en" for English.

3.11 Size information

   Inserted by certain mailers to       Content-       Non-standard,
   indicate the size in bytes of the    Length:        discouraged.
   message text. This is part of a
   format some mailers use when
   showing a message to its users,
   and this header should not be
   used when sending a message
   through the net. The use of this
   header in transmission of a
   message can cause several
   robustness and interoperability

   Size of the message.                 Lines:         RFC 1036: 2.2.12,
                                                       not standardized
                                                       for use in e-mail.

3.12 Conversion control

   The body of this message may not     Conversion:    RFC 1327, not for
   be converted from one character                     general usage.
   set to another. Values:
   Prohibited and allowed.

   Non-standard variant of              Content-       Non-standard.
   Conversion: with the same values.    Conversion:

   The body of this message may not     Conversion-    RFC 1327, not for
   be converted from one character      With-Loss:     general usage.
   set to another if information
   will be lost. Values: Prohibited
   and allowed.

3.13 Encoding information

   Format of content (character set     Content-Type:  RFC 1049,
   etc.) Note that the values for                      RFC 1123: 5.2.13,
   this header are defined in                          RFC 1521: 4.
   different ways in RFC 1049 and in                   RFC 1766: 4.1
   MIME (RFC 1521), look for the
   "MIME-version" header to
   understand if Content-Type is to
   be interpreted according to RFC
   1049 or according to MIME. The
   MIME definition should be used in
   generating mail.

   RFC 1766 defines a parameter
   "difference" to this header.

   Information from the SGML entity     Content-SGML-  non-standard
   declaration corresponding to the     Entity:
   entity contained in the body of
   the body part.

   Coding method used in a MIME         Content-       RFC 1521: 5.
   message body.                        Transfer-

   Only used with the value             Message-Type:  RFC 1327, not for
   "Delivery Report" to indicates                      general usage.
   that this is a delivery report
   gatewayed from X.400.

   Used in several different ways by    Encoding:      RFC 1154,
   different mail systems. Some use                    RFC 1505,
   it for a kind of content-type                       experimental.
   information, some for encoding
   and length information, some for
   a kind of boundary information,
   some in other ways.

3.14 Resent-headers

   When manually forwarding a           Resent-Reply-  RFC 822: C.3.3.
   message, headers referring to the    To:,
   forwarding, not to the original      Resent-From:,
   message.  Note: MIME specifies       Resent-
   another way of resending             Sender:,
   messages, using the "Message"        Resent-From:,
   Content-Type.                        Resent-Date:,

3.15 Security and reliability

   Checksum of content to ensure        Content-MD5:   RFC 1864, proposed
   that it has not been modified.                      standard.

   Used in Usenet News to store         Xref:          RFC 1036: 2.2.13,
   information to avoid showing a                      only in Usenet
   reader the same article twice if                    News, not in e-
   it was sent to more than one                        mail.
   newsgroup. Only for local usage
   within one Usenet News server,
   should not be sent between

3.16 Miscellaneous

   Name of file in which a copy of      Fcc:           Non-standard.
   this message is stored.

   Has been automatically forwarded.    Auto-          RFC 1327, not for
                                        Forwarded:     general usage.

   Can be used in Internet mail to      Discarded-     RFC 1327, not for
   indicate X.400 IPM extensions        X400-IPMS-     general usage.
   which could not be mapped to         Extensions:
   Internet mail format.

   Can be used in Internet mail to      Discarded-     RFC 1327, not for
   indicate X.400 MTS extensions        X400-MTS-      general usage.
   which could not be mapped to         Extensions:
   Internet mail format.

   This field is used by some mail      Status:         Non-standard,
   delivery systems to indicate the                     should never
   status of delivery for this                          appear in mail in
   message when stored. Common                          transit.
   values of this field are:

   U    message is not downloaded
        and not deleted.

   R    message is read or

   O    message is old but not

   D    to be deleted.

   N    new (a new message also
        sometimes is distinguished
        by not having any "Status:"

   Combinations of these characters
   can occur, such as "Status: OR"
   to indicate that a message is
   downloaded but not deleted.

4. Acknowledgments

   Harald Tveit Alvestrand, Ned Freed, Olle Jdrnefors, Keith Moore, Nick
   Smith and several other people have helped me with compiling this
   list.  I especially thank Ned Freed and Olle Jdrnefors for their
   thorough review and many helpful suggestions for improvements. I
   alone take responsibility for any errors which may still be in the

   An earlier version of this list has been published as part of [13].

5. References

Ref.    Author, title                                    IETF status
                                                         (July 1996)
-----   ---------------------------------------------    -----------
[1]     J. Postel: "Simple Mail Transfer Protocol",      Standard,
        STD 10, RFC 821, August 1982.                    Recommended

[2]     D. Crocker: "Standard for the format of ARPA     Standard,
        Internet text messages." STD 11, RFC 822,        Recommended
        August 1982.

[3]     M.R. Horton, R. Adams: "Standard for             Not an offi-
        interchange of USENET messages", RFC 1036,       cial IETF
        December 1987.                                   standard,
                                                         but in
                                                         reality a de-
                                                         standard for
                                                         Usenet News

[4]     M. Sirbu: "A Content-Type header header for      Standard,
        internet messages", RFC 1049, March 1988.        Recommended,
                                                         but can in
                                                         the future
                                                         be expected
                                                         to be
                                                         replaced by

[5]     R. Braden (editor): "Requirements for            Standard,
        Internet Hosts -- Application and Support",      Required
        STD-3, RFC 1123, October 1989.

[6]     D. Robinson, R. Ullman: "Encoding Header         Non-standard
        Header for Internet Messages", RFC 1154,
        April 1990.

[7]     S. Hardcastle-Kille: "Mapping between            Proposed
        X.400(1988) / ISO 10021 and RFC 822",  RFC       standard,
        1327 May 1992.                                   elective

[8]     H. Alvestrand & J. Romaguera: "Rules for         Proposed
        Downgrading Messages from X.400/88 to            standard,
        X.400/84 When MIME Content-Types are Present     elective
        in the Messages", RFC 1496, August 1993.

[9]     A. Costanzo: "Encoding Header Header for         Non-standard
        Internet Messages", RFC 1154, April 1990.

[10]    A. Costanzo, D. Robinson: "Encoding Header       Experimental
        Header for Internet Messages", RFC 1505,
        August 1993.

[11]    N. Borenstein & N. Freed: "MIME (Multipurpose    Draft
        Internet Mail Extensions) Part One:              Standard,
        Mechanisms for Specifying and Describing the     elective
        Format of Internet Message Bodies", RFC 1521,
        Sept 1993.

[12]    H. Alvestrand: "Tags for the Identification      Proposed
        of Languages", RFC 1766, February 1995.          standard,

[13]    J. Palme: "Electronic Mail", Artech House        Non-standard
        publishers, London-Boston January 1995.

[14]    R. Troost, S. Dorner: "Communicating             Experimental
        Presentation Information in Internet
        Messages: The Content-Disposition Header",
        RFC 1806, June 1995.

[15]    B. Kantor, P. Lapsley, "Network News Transfer    Proposed
        Protocol: "A Proposed Standard for the Stream-   standard
        Based Transmission of News", RFC 977, January

[16]    1848  PS   S. Crocker, N. Freed, J. Galvin,      Proposed
        S. Murphy, "MIME Object Security Services",      standard
        RFC 1848, March 1995.

[17]    J. Myers, M. Rose: The Content-MD5 Header        Draft
        Header, RFC 1864, October 1995.                  standard

[18]    M. Horton, UUCP mail interchange format          Not an offi-
        standard, RFC 976, Januari 1986.                 cial IETF
                                                         but in
                                                         reality a de-
                                                         standard for
                                                         Usenet News

[19]    T. Berners-Lee, R. Headering, H. Frystyk:        Not an official
        Hypertext Transfer Protocol -- HTTP/1.0,         IETF standard,
        RFC 1945, May 1996.                              but the defacto
                                                         standard until
                                                         the next
                                                         version is

[20]    G. Vaudreuil: Voice Profile for Internet         Experimental
        Mail, RFC 1911, February 1996.

[21]    H. Spencer: News Article Format and              Not even an
        Transmission, June 1994,                         RFC, but
        FTP://zoo.toronto.edu/pub/news.ps                still widely
        FTP://zoo.toronto.edu/pub/news.txt.Z             used and
        This document is often referenced under the      almost a de-
        name "son-of-RFC1036".                           facto
                                                         standard for
                                                         Usenet News

6. Author's Address

   Jacob Palme                          Phone: +46-8-16 16 67
   Stockholm University/KTH             Fax: +46-8-783 08 29
   Electrum 230                         E-mail: jpalme@dsv.su.se
   S-164 40 Kista, Sweden

Appendix A:
   Headers sorted by Internet RFC document in which they appear.

   RFC 822


   RFC 976

   "From " (followed by space, not colon (:")

   RFC 1036


   RFC 1049


   RFC 1327

   Message-Type Delivery

   RFC 1505


   RFC 1521


   RFC 1806


   RFC 1864


   RFC 1911


   son-of-RFC1036 [21]


   Not Internet standard

   "From " (not followed by ":")

Appendix B:
   Alphabetical index

   Section Heading-header
   ------- --------------

   3.3     Also-Control
   3.3     Alternate-Recipient
   3.4     Apparently-To
   3.4     Approved
   3.6     Article-Names
   3.6     Article-Updates
   3.16    Auto-Forwarded
   3.4     bcc
   3.4     cc
           Client, see Originating-Client
   3.6     Content-Base
   3.12    Content-Conversion
   3.7     Content-Description
   3.3     Content-Disposition
   3.6     Content-ID
   3.7     Content-Identifier
   3.10    Content-Language see also Language
   3.11    Content-Length
   3.6     Content-Location
   3.15    Content-MD5
   3.4     Content-Return
   3.13    Content-SGML-Entity
   3.13    Content-Transfer-Encoding
   3.13    Content-Type
   3.3     Control
   3.12    Conversion
   3.12    Conversion-With-Loss
   3.8     Date
   3.8     Delivery-Date
           Delivery-Report, see Generate-Delivery-Report, Prevent-
           Delivery-Report, Non-Delivery-Report, Content-Type
           Description, see Content-Description
   3.16    Discarded-X400-IPMS-Extensions
   3.16    Discarded-X400-MTS-Extensions
   3.3     Disclose-Recipients
           Disposition, see Content-Disposition
   3.4     Distribution
   3.2     DL-Expansion-History-Indication
   3.13    Encoding see also Content-Transfer-Encoding
   3.4     Errors-To

   3.8     Expires
           Extension see Discarded-X400-IPMS-Extensions, Discarded-
   3.4     Fax
   3.16    Fcc
   3.4     Followup-To
           Forwarded, see Auto-Forwarded
   3.4     For-Comment
   3.4     For-Handling
   3.4     From
   3.4     Generate-Delivery-Report
           History, see DL-Expansion-History-Indication
           ID, see Content-ID and Message-ID
           Identifier, see Content-ID and Message-ID
   3.9     Importance
   3.6     In-Reply-To
   3.9     Incomplete-Copy
   3.7     Keywords
   3.10    Language see also Content-Language
           Length see Content-Length
   3.11    Lines
   3.4     Mail-System-Version see also X-mailer
   3.4     Mailer
           MD5 see Content-MD5
   3.6     Message-ID
   3.13    Message-Type
   3.3     MIME-Version
   3.4     Newsgroups
           Newsreader, see X-Newsreader
   3.6     Obsoletes
   3.7     Organisation
   3.7     Organization
   3.3     Original-Encoded-Information-Types
   3.4     Originating-Client
   3.2     Path
   3.4     Phone
   3.9     Precedence
   3.4     Prevent-NonDelivery-Report
   3.9     Priority
   3.2     Received
           Recipient, see To, cc, bcc, Alternate-Recipient, Disclose-
   3.6     References
   3.8     Reply-By
   3.4     Reply-To, see also In-Reply-To, References
   3.14    Resent-
           Return see also Content-Return
   3.2     Return-Path

   3.5     Return-Receipt-To
   3.6     See-Also
   3.4     Sender
   3.9     Sensitivity
   3.16    Status
   3.7     Subject
   3.7     Summary
   3.6     Supersedes
   3.4     Telefax
   3.4     To
           Transfer-Encoding see Content-Transfer-Encoding
           Type see Content-Type, Message-Type, Original-Encoded-
           Version, see MIME-Version, X-Mailer
   3.4     X400-Content-Return
   3.4     X-Mailer see also Mail-System-Version
   3.4     X-Newsreader
   3.15    Xref


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