Internet Draft
Network Working Group Jacob Palme
Internet Draft Stockholm University/KTH
draft-palme-mailext-headers-01.txt Sweden
Category: Informational Date: May 1999
Revision of: RFC 2076 Expires: November 1999
Common Internet Message Header Fields
Status of this Memo
This document is an Internet-Draft and is in full conformance
with all provisions of Section 10 of RFC2026.
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
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documents at any time. It is inappropriate to use Internet-
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"work in progress."
The list of current Internet-Drafts can be accessed at
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Copyright (C) The Internet Society 1998. All Rights Reserved.
Abstract
This memo contains a table of commonly occurring header fields 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
1766, RFC 1806, RFC 1864, RFC 1911 and RFC 2045. A few commonly
occurring header fields which are not defined in RFCs are also
included. For each header field, the memo gives a short description and
a reference to the RFC in which the header field is defined.
This document is a revision of RFC 2076. The following new header
fields, not included in RFC 2076, have been added:
Also-Control, Content-Alias, Content-Conversion, Content-Features,
Disposition-Notification-Options, Disposition-Notification-To, Expiry-
Date, For-Approval, List-Archive, List-Help, List-ID, List-Owner, List-
Post, List-Software, List-Subscribe, List-Unsubscribe, Original-
Recipient, Originator, Originator-Info, Path, PICS-Label, Replaces,
Speech-Act, Translated-By. Translation-Of, X-Envelope-From, X-Envelope-
To, X-List-Host, X-Listserver, X-MIME-Autoconverted, X-No-Archive, X-
Priority, X-Sender, X-X-Sender, X-UIDL, X-URL, X-URI.
The latest, revised version of this document is available in plain
text, HTML and Adobe Acrobat format at URL
http://www.dsv.su.se/~jpalme/ietf/jp-ietf-home.html#anchor1003783
Table of contents
Abstract 1
1. Introduction 3
2. Use of gatewaying header fields 6
3. Table of header fields 6
3.1 Phrases used in the tables 6
3.2 Trace information 8
3.3 Format and control information 8
3.4 Sender and recipient indication 9
3.5 Response control 14
3.6 Message identification and referral header fields 17
3.7 Other textual header fields 19
3.8 Header fields containing dates and times 20
3.9 Quality information 20
3.10 Language information 21
3.11 Size information 22
3.12 Conversion control 22
3.13 Encoding information 22
3.14 Resent-header fields 24
3.15 Security and reliability 24
3.16 Mailing list control 25
3.17 Miscellaneous 26
4. Acknowledgments 27
Copyright and disclaimer 28
5. References 28
6. Author's address 31
Appendix A: Header fields sorted by Internet RFC document in
which they appear. 31
RFC 822 31
RFC 976 32
RFC 1036 32
RFC 1049 33
RFC 1327 33
RFC 1505 33
RFC 2045 33
RFC 1806 34
RFC 1911 34
RFC 2110 34
RFC 2369 34
son-of-RFC1036 [21] 34
draft-ietf-receipt 35
World Wide Web Consortium (W3C) Recommendations 35
Not Internet standard 35
Appendix B: Alphabetical index 36
1. Introduction
Many different Internet standards and RFCs define header fields which
may occur on Internet Mail Messages and Usenet News Articles. The
intention of this document is to list all such header fields in one
document as an aid to people developing message systems or interested
in Internet Mail standards.
The document contains all header fields 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 2045 [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 header fields only
appear inside the body of a message, and thus are not header fields 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. Some additional header fields which often can be
found in e-mail headings but are not part of any Internet standard are
also included.
For each header field, the document gives a short description and a
reference to the Internet standard or RFC, in which they are defined.
The header field names given here are spelled the same way as when they
are actually used. This is usually American but sometimes English
spelling. One header field in particular, "Organisation/Organization",
occurs in e-mail header fields sometimes with the English and other
times with the American spelling.
The following words are used in this memo with the meaning specified
below:
heading Formatted text at the top of a message, ended by a
blank line
header field One field in the heading, beginning with a field
name, colon, and followed by the field value(s). The
words "heading field" and "header" are also
sometimes used with this meaning.
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
http://www.dsv.su.se/~jpalme/ietf/ietf-mail-attributes.html
http://www.dsv.su.se/~jpalme/ietf/mail-attributes.html and
http://www.dsv.su.se/~jpalme/ietf/mail-attributes.pdf
Please e-mail me (Jacob Palme ) if you have noted
header fields which should be included in this memo but are not.
2. Use of gatewaying header fields
RFC 1327 defines a number of new header fields in Internet mail, which
are defined to map header fields which X.400 has but which were
previously not standardized in Internet mail. The fact that a header
field 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 field is recommended for messages wholly within
Internet mail. Some of these header fields 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.
Header fields 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 header fields are not standardized for use in
Internet e-mail and should be handled with caution by e-mail agents.
3. Table of header fields
3.1 Phrases used in the tables
"not for general Used to mark header fields which are defined
usage" in RFC 1327 for use in messages from or to
Internet mail/X.400 gateways. These header
fields have not been standardized for general
usage in the exchange of messages between
Internet mail-based systems.
"not standardized Used to mark header fields defined only in RFC
for use in e-mail" 1036 for use in Usenet News. These header
fields 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 field is not specified in any of
referenced RFCs which define Internet
protocols, including Internet Standards, draft
standards or proposed standards. The header
field appears here because it often appears in
e-mail or Usenet News. Usage of these header
fields is not in general recommended. Some
header field proposed in ongoing IETF
standards development work, but not yet
accepted, are also marked in this way.
"discouraged" This header field, which is non-standard, is
known to create problems and should not be
generated. Handling of such header fields in
incoming mail should be done with great
caution.
"controversial" The meaning and usage of this header field is
controversial, i.e. different implementors
have chosen to implement the header field in
different ways. Because of this, such header
fields should be handled with caution and
understanding of the different possible
interpretations.
"experimental" This header field is used for newly defined
header fields, 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-
mail.
Trace of distribution lists DL-Expansion- RFC 1327, not for
passed. History- general usage.
Indication:
3.3 Format and control information
An indicator that this message is MIME-Version: RFC 2045: 4.
formatted according to the MIME
standard, and an indication of
which version of MIME is
utilized.
Only in Usenet News, contains Control: RFC 1036: 2.1.6,
commands to be performed by News only in Usenet
agents. News, not in e-
mail.
Special Usenet News commands and Also-Control: son-of-RFC1036
a normal article at the same [21], non-
time. 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.
Information-
Types:
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:
Allowed.
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: header fields.
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 field (not followed by
":") below.
(1) This header field should From (not not standardized
never appear in e-mail being followed by a for use in e-mail
sent, and should thus not appear colon)
in this memo. It is however
included, since people often ask
about it.
This header field 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 field 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
field 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. (not followed
by a colon)
Sometimes called "From_" header
field.
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, RFC
header field. Should be 1036.
authenticated,
according to RFC 822, but what
kind of authentication is not
clear. Some implementations
expect that the e-mail address
used in this field can be used to
reach the sender, others do not.
See also "X-Sender".
Sometimes used in Usenet News in Originator: Non-standard
similar ways to "Sender:"
Some mail software expect X-Sender: Non-standard
"Sender:" to be an e-mail address
which you can send mail to.
However, some mail software has
as the best authenticated sender
a POP or IMAP account, which you
might not be able to send to.
Because of this, some mail
software put the POP or IMAP
account into an X-sender header
field instead of a Sender header
field, to indicate that you may
not be able to send e-mail to
this address. See also "X-X-
Sender".
Another use of" X-Sender:" is
that some e-mail software, which
wants to insert a "Sender:"
header, will first change an
existing "Sender:" header to "X-
Sender". This use is actually
often the same as that described
in the previous paragraph, since
the new "Sender:" is added
because it is better
authenticated than the old value.
Even though some systems put the X-X-Sender: Non-standard
POP or IMAP account name into the
"X-Sender:" instead of the Sender
header field, some mail software
tries to send to the "X-Sender:"
too. To stop this, some systems
have begun to use "X-X-Sender:"
to indicate an authentication of
the sender which might not be
useable to send e-mail to. See
also "Originator-Info:"
Contains information about the Originator- Non-standard [25]
authentication of the originator Info:
in a format which is not easily
used to send email to, to avoid
the problems with "Sender" and "X-
Sender".
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.
Primary recipients, who are For-Approval: Non-standard
requested to approve 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
field also in e-mail although it for use in e-mail.
is not standardized there.
Unfortunately, the header field
can appear in e-mail with three
different and contradictory
meanings:
(a) Indicating the newsgroup
recipient of an article/message
sent to both e-mail and Usenet
News recipients.
(b) In a message adressed to some
mail to news gateways, indicates
the newsgroup(s) that the message
is to be posted to.
(c) In a personally addressed
reply to an article in a news-
group, indicating the newsgroup
in which this discussion
originated.
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
recipients.
Geographical or organizational Distribution: RFC 1036: 2.2.7,
limitation on where this article not standardized
can be distributed. Value can be for use in e-mail.
a compete or incomplete domain
names, also various special
values are accepted like "world",
"usenet", "USA", etc.
Fax number of the originator. Fax:, Non-standard.
Telefax:
Phone number of the originator. Phone: Non-standard.
If the recipient in the envelope X-Envelope-To Non-standard.
(SMTP "MAIL FROM") is not
included in the CC list, some
mail servers add this to the
RFC822 header field as an aid to
clients which would otherwise not
be able to display the envelope
recipients.
If the sender in the envelope X-Envelope- Non-standard.
(SMTP "RCTP TO") is not the same From
as the senders in the "From" or
"Sender" RFC822 header fields,
some mail servers add this to the
RFC822 header fields as an aid to
clients which would otherwise not
be able to display this
information.
Information about the client Mail-System- Non-standard.
software of the originator. Version:,
Mailer:,
Originating-
Client:, X-
Mailer, X-
Newsreader
3.5 Response control
This header field is meant to Reply-To: RFC 822: 4.4.3,
indicate where the sender wants RFC 1036: 2.2.1
replies to go. Unfortunately, controversial.
this is 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
field 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 field. These
practices are controversial. The
personal opinion of the author of
this RFC is that this header
field 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 field 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 field
does not say anything about where
follow-up in e-mail is to be
sent.
Note that the value of this
header field must always be one
or more newsgroup names, never e-
mail addresses.
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 MAIL FROM 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:
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:
Indicate that the sender wants a Disposition- RFC 2298
dispoisition notification when Notification-
this message is received (read, To
processed, etc.) by its
receipents.
For future options on disposition Disposition- RFC 2298
notifications. Notification-
Options
Original Recipient information Original- RFC 2298
for inclusion in disposition Recipient
notifications.
3.6 Message identification and referral header fields
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 2045: 7.
content of a message.
Base to be used for resolving Content-Base: RFC 2110
relative URIs within this content
part.
URI with which the content of Content- RFC 2110
this content part might be Location:
retrievable.
Used in addition to Content- Content- Work in progress
Location if this content part can Alias:
be retrieved through more than
one URI. Only one of them is
allowed in the Content-Location,
the other can be specified in
Content-Alias.
Sometimes used with the same X-URL: Non-standard
meaning as "Content-Location:",
sometimes to indicate the web
home page of the sender or of his
organisation.
Similar usage as "X-URL". The URI X-URI: Non-standard
can be either a URL or a URN.
URNs are meant to become more
persistent references to
resources than URLs.
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 field 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.
Still another name for similar Replaces: non-standard,
functionality as for "Obsoletes:" proposed in IETF
and "Supersedes:". This may USEFOR working
become the most recommended group
header in the future, but is
still under discussion in IETF
standards development work.
Unique identifier for a message, X-UIDL: non-standard
local to a particular local
mailbox store. The UIDL
identifier is defined in the POP3
standard, but not the "X-UIDL:"
header.
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
Newsgroup.
Reference to the Message-ID of a Translation- non-standard
message, which the current Of:
message is a translation of.
Mailbox of the person who made Translated- non-standard
the translation. By:
3.7 Other textual header fields
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 2045: 8.
part of a message, for example a Description:
caption for an image body part.
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
field 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 Header fields 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
submitted.
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.
Values: 1 (Highest), 2 (High), 3 X-Priority: Non-standard [24]
(Normal), 4 (Low), 5 (Lowest). 3
(Normal) is default if the field
is omitted.
Sometimes used as a priority Precedence: Non-standard,
value which can influence controversial.
transmission speed and delivery.
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 field 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.
Ratings label to control PICS-Label: REC-PICS-labels,
selection (filtering) of messages W3C document [23].
according to the PICS protocol.
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 field should not
be used when sending a message
through the net. The use of this
header field in transmission of a
message can cause several
robustness and interoperability
problems.
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 field are defined in RFC 2045: 5.
different ways in RFC 1049 and in RFC 1766: 4.1
MIME (RFC 2045), look for the
"MIME-version" header field 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
field.
Various other Content-Type define
various additional parameters.
For example, the parameter
"charset" is mandatory for all
textual Content-Types.
Can give more detailed Content- non-standard
information about the Content- Features:
Type. Example:
(& (color=binary)
(image-file-structure=TIFF-S)
(dpi=200)
(paper-size=A4)
(image-coding=MH)
(MRC-mode=0)
(ua-media=stationery) )
This header is meant to be used
when you can choose between
different versions of a resource,
such as when using
multipart/atlernative.
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 2045: 6.
message body. Transfer-
Encoding:
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.
Information about conversion of X-MIME- non-standard
this message on the path from Autoconverted:
sender to recipient, like
conversion between MIME encoding
formats. Note: Auto-conversion
may invalidate digital seals and
signatures.
3.14 Resent-header fields
When manually forwarding a Resent-Reply- RFC 822: C.3.3.
message, header fields referring To:,
to the forwarding, not to the Resent-From:,
original message. Note: MIME Resent-
specifies another way of Sender:,
resending messages, using the Resent-From:,
"Message" Content-Type. Resent-Date:,
Resent-To:,
Resent-cc:,
Resent-bcc:,
Resent-
Message-ID:
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
servers.
3.16 Mailing list control
Contains URL to use to get a List- RFC 2369 [26]
subscription to the mailing list Subscribe
from which this message was
relayed.
Contains URL to use to List- RFC 2369 [26]
unsubscribe the mailing list from Unsubscribe
which this message was relayed.
Contains URL to send e-mail to List-Owner RFC 2369 [26]
the owner of the mailing list
from which this message was
relayed.
Contains URL to use to get a List-Help RFC 2369 [26]
information about the mailing
list from which this message was
relayed.
Contains URL to use to send List-Post RFC 2369 [26]
contributions to the mailing list
from which this message was
relayed.
Contains URL to use to browse the List-Archive RFC 2369 [26]
archives of the mailing list from
which this message was relayed.
Information about the software List-Software Non-standard, has
used in a mailing list expander been considered
through which this message has for inclusion in
passed. [26].
Stores the URN of the mailing List-ID Non-standard, has
list, through which this message been considered
was distributed. for inclusion in
[26].
Information about the software X-Listserver Non-standard.
used in a mailing list expander
through which this message has
passed. Warning: "Listserv" is a
trademark and should not be used
for other than the "Listserv"
product. Use, instead the "List-
Software" header field.
3.17 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
downloaded.
O message is old but not
deleted.
D to be deleted.
N new (a new message also
sometimes is distinguished
by not having any "Status:"
header field.
Combinations of these characters
can occur, such as "Status: OR"
to indicate that a message is
downloaded but not deleted.
Do not archive this message in X-No-Archive: Non-standard
publicly available archives. Yes
Speech act categoriztion of a Speech-Act: Non-standard
message, examples of speeach acts
are Question, Idea, More,
Promise, Sad, Happy, Angry,
summary, Decision
4. Acknowledgments
Harald Tveit Alvestrand, Ned Freed, Olle J„rnefors, Keith Moore, Nick
Smith and several other people have helped me with compiling this list.
I especially thank Ned Freed and Olle J„rnefors for their thorough
review and many helpful suggestions for improvements. I alone take
responsibility for any errors which may still be in the list.
An earlier version of this list has been published as part of [13].
Copyright and disclaimer
The IETF takes no position regarding the validity or scope of
any intellectual property or other rights that might be
claimed to pertain to the implementation or use of the
technology described in this document or the extent to which
any license under such rights might or might not be available;
neither does it represent that it has made any effort to
identify any such rights. Information on the IETF's procedures
with respect to rights in standards-track and standards-
related documentation can be found in BCP-11. Copies of claims
of rights made available for publication and any assurances of
licenses to be made available, or the result of an attempt
made to obtain a general license or permission for the use of
such proprietary rights by implementors or users of this
specification can be obtained from the IETF Secretariat."
The IETF invites any interested party to bring to its
attention any copyrights, patents or patent applications, or
other proprietary rights which may cover technology that may
be required to practice this standard. Please address the
information to the IETF Executive Director.
Copyright (C) The Internet Society (date). All Rights
Reserved.
This document and translations of it may be copied and
furnished to others, and derivative works that comment on or
otherwise explain it or assist in its implmentation may be
prepared, copied, published and distributed, in whole or in
part, without restriction of any kind, provided that the above
copyright notice and this paragraph are included on all such
copies and derivative works. However, this document itself may
not be modified in any way, such as by removing the copyright
notice or references to the Internet Society or other Internet
organizations, except as needed for the purpose of developing
Internet standards in which case the procedures for copyrights
defined in the Internet Standards process must be followed, or
as required to translate it into languages other than English.
The limited permissions granted above are perpetual and will
not be revoked by the Internet Society or its successors or
assigns.
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-
facto
standard for
Usenet News
[4] M. Sirbu: "A Content-Type header field header Standard,
field for internet messages", RFC 1049, March Recommended,
1988. but can in
the future
be expected
to be
replaced by
MIME
[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
field Header field 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 field Header Non-standard
field for Internet Messages", RFC 1154, April
1990.
[10] A. Costanzo, D. Robinson: "Encoding Header Experimental
field Header field for Internet Messages",
RFC 1505, August 1993.
[11] N. Freed & N. Borenstein: "MIME (Multipurpose Draft
Internet Mail Extensions) Part One: Format of Standard,
Internet Message Bodies. RFC 2945. November elective
1996.
[12] H. Alvestrand: "Tags for the Identification Proposed
of Languages", RFC 1766, February 1995. standard,
elective
[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
field", 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
1986.
[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
field Header field, RFC 1864, October 1995. standard
[18] M. Horton, UUCP mail interchange format Not an offi-
standard, RFC 976, Januari 1986. cial IETF
standard,
but in
reality a de-
facto
standard for
Usenet News
[19] T. Berners-Lee, R. Header fielding, H. Informatio
Frystyk: Hypertext Transfer Protocol -- nal
HTTP/1.0, RFC 1945.
[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.Z still widely
FTP://zoo.toronto.edu/pub/news.txt.Z used and
partly
This document is often referenced under the almost a de-
name "son-of-RFC1036". facto
standard for
Usenet News
[23] PICS Label Distribution Label Syntax and Other
Communication Protocols, World Wide Web standard
Consortium, October 1996.
[24] Eudora Pro Macintosh User Manual, Qualcomm Non-standard
Inc., 1988-1995.
[25] C. Newman: Originator-Info Message Header Non-standard
field. work in progress, July 1997.
[26] Grant Neufeld and Joshua D. Baer: The Use of Proposed
URLs as Meta-Syntax for Core Mail List standard
Commands and their Transport through Message
Header fields, RFC 2369, July 1998..
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:
Header fields sorted by Internet RFC document in which they appear.
RFC 822
-------
bcc
cc
Comments
Date
From
In-Reply-To
Keywords
Message-ID
Received
References
Reply-To
Resent-
Resent-bcc
Resent-cc
Resent-Date
Resent-From
Resent-From
Resent-Message-ID
Resent-Reply-To
Resent-To
Return-Path
Sender
Sender
Subject
To
RFC 976
-------
"From " (followed by space, not colon (:")
RFC 1036
--------
Approved
Control
Distribution
Expires
Followup-To
Lines
Newsgroups
Organization
Path
Summary
Xref
RFC 1049
--------
Content-Type
RFC 1327
--------
Alternate-recipient
Auto-Forwarded
Autoforwarded
Content-Identifier
Content-Return
Conversion
Conversion-With-Loss
Delivery-Date
Discarded-X400-IPMS-Extensions
Discarded-X400-MTS-Extensions
Disclose-Recipients
DL-Expansion-History
Expiry-Date
Generate-Delivery-Report
Importance
Incomplete-Copy
Language
Message-Type Delivery
Obsoletes
Original-Encoded-Information-Types
Prevent-NonDelivery-Report
Priority
Reply-By
Report
Sensitivity
RFC 1505
--------
Encoding
RFC 2045
--------
Content-Description
Content-ID
Content-Transfer-Encoding
Content-Type
MIME-Version
RFC 1806
--------
Content-Disposition
RFC 1864
--------
Content-MD5
RFC 1911
--------
Importance
Sensitivity
RFC 2110
--------
Content-Base
Content-Location
RFC 2369
--------
List-Archive
List-Help
List-Owner
List-Post
List-Software
List-Subscribe
List-Unsubscribe
son-of-RFC1036 [21]
-------------------
Also-Control
Article-Names
Article-Updates
See-Also
Supersedes
draft-ietf-receipt
------------------
Disposition-Notification-To
Disposition-Notification-Options
Original-Recipient
World Wide Web Consortium (W3C) Recommendations
-----------------------------------------------
Pics-Label
Not Internet standard
---------------------
"From " (not followed by ":")
Apparently-to
Content-Alias
Content-Length
Content-SGML-Entity
Encoding
Errors-To
Fax
Fcc
For-Approval
For-Comment
For-Handling
List-ID
Mail-System-Version
Mailer
Organisation
Originating-Client
Originator-Info
Phone
Return-Receipt-To
Speech-Act
Status
Supersedes
Telefax
Translated-By
Translation-Of
X-Envelope-From
X-Envelope-To
X-Mailer
X-MIME-Autoconverted
X-Newsreader
X-No-Archive
X-Priority
X-Sender
X-UIDL
X-URI
X-URL
X-X-Sender
X400-Content-Return
Appendix B: Alphabetical index
Section Header field
------- ------------
3.3 Also-Control
3.3 Alternate-Recipient
3.4 Apparently-To
3.4 Approved
3.6 Article-Names
3.6 Article-Updates
3.17 Auto-Forwarded
3.4 bcc
3.4 cc
Client, see Originating-Client
Comment, see For-Comment
3.7 Comments
3.6 Content-Alias
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
Copy, see Incomplete-Copy
3.8 Date
Date, see also Delivery-Date, Received, Expires, Expiry-
Date
3.8 Delivery-Date
Delivery-Report, see Generate-Delivery-Report, Prevent-
Delivery-Report, Non-Delivery-Report, Content-Type
Description, see Content-Description
3.17 Discarded-X400-IPMS-Extensions
3.17 Discarded-X400-MTS-Extensions
3.3 Disclose-Recipients
Disposition, see also Content-Disposition
3.5 Disposition-Notification-Options
3.5 Disposition-Notification-To
3.4 Distribution
3.2 DL-Expansion-History-Indication
3.13 Encoding see also Content-Transfer-Encoding
3.4 Errors-To
3.8 Expires
3.8 Expiry-Date
Extension see Discarded-X400-IPMS-Extensions, Discarded-
X400-MTS-Extensions
3.4 Fax
3.17 Fcc
3.4 Followup-To
3.4 For-Approval
3.4 For-Comment
3.4 For-Handling
Forwarded, see Auto-Forwarded
3.4 From
3.4 Generate-Delivery-Report
Handling, see For-Handling
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
Label, see PICS-Label
3.10 Language see also Content-Language
Length see Content-Length
3.11 Lines
3.16 List-Archive
3.16 List-Help
3.16 List-ID
3.16 List-Owner
3.16 List-Post
3.16 List-Software
3.16 List-Subscribe
3.16 List-Unsubscribe
Loss, see Conversion-With-Loss
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
3.6 Original-Recipient
3.4 Originating-Client
3.4 Originator-Info see also Sender
3.2 Path
3.4 Phone
3.9 PICS-Label
3.9 Precedence
3.4 Prevent-NonDelivery-Report
3.9 Priority
3.2 Received
Recipient, see To, cc, bcc, Alternate-Recipient, Disclose-
Recipient
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
3.17 Speech-Act
3.17 Status
3.7 Subject
3.7 Summary
3.6 Supersedes
3.4 Telefax
3.4 To
Transfer-Encoding see Content-Transfer-Encoding
3.6 Translated-By
3.6 Translation-Of
Type see Content-Type, Message-Type, Original-Encoded-
Information-Types
Version, see MIME-Version, X-Mailer
3.4 X-Envelope-From
3.4 X-Envelope-To
3.16 X-List-Host
3.16 X-Listserver
3.4 X-Mailer see also Mail-System-Version
3.13 X-MIME-Autoconverted
3.4 X-Newsreader
3.17 X-No-Archive
3.9 X-Priority
3.4 X-Sender see also Originator-Info
3.6 X-UIDL
3.6 X-URI
3.6 X-URL see also Content-Location
3.4 X-X-Sender see also Originator-Info
3.4 X400-Content-Return
3.15 Xref