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Network Working Group                                       P. HoffmanRequest for Comments: 2368                    Internet Mail ConsortiumUpdates:1738,1808                                        L. MasinterCategory: Standards Track                            Xerox Corporation                                                           J. Zawinski                                               Netscape Communications                                                             July 1998The mailto URL schemeStatus of this Memo   This document specifies an Internet standards track protocol for the   Internet community, and requests discussion and suggestions for   improvements.  Please refer to the current edition of the "Internet   Official Protocol Standards" (STD 1) for the standardization state   and status of this protocol.  Distribution of this memo is unlimited.Copyright Notice   Copyright (C) The Internet Society (1998).  All Rights Reserved.Abstract   This document defines the format of Uniform Resource Locators (URL)   for designating electronic mail addresses. It is one of a suite of   documents which replaceRFC 1738, 'Uniform Resource Locators', andRFC 1808, 'Relative Uniform Resource Locators'. The syntax of   'mailto' URLs fromRFC 1738 is extended to allow creation of moreRFC822 messages by allowing the URL to express additional header and   body fields.1. Introduction   The mailto URL scheme is used to designate the Internet mailing   address of an individual or service. In its simplest form, a mailto   URL contains an Internet mail address.   For greater functionality, because interaction with some resources   may require message headers or message bodies to be specified as well   as the mail address, the mailto URL scheme is extended to allow   setting mail header fields and the message body.2. Syntax of a mailto URL   Following the syntax conventions ofRFC 1738 [RFC1738], a "mailto"   URL has the form:Hoffman, et. al.            Standards Track                     [Page 1]

RFC 2368                 The mailto URL scheme                 July 1998     mailtoURL  =  "mailto:" [ to ] [ headers ]     to         =  #mailbox     headers    =  "?" header *( "&" header )     header     =  hname "=" hvalue     hname      =  *urlc     hvalue     =  *urlc   "#mailbox" is as specified inRFC 822 [RFC822]. This means that it   consists of zero or more comma-separated mail addresses, possibly   including "phrase" and "comment" components. Note that all URL   reserved characters in "to" must be encoded: in particular,   parentheses, commas, and the percent sign ("%"), which commonly occur   in the "mailbox" syntax.   "hname" and "hvalue" are encodings of anRFC 822 header name and   value, respectively. As with "to", all URL reserved characters must   be encoded.   The special hname "body" indicates that the associated hvalue is the   body of the message. The "body" hname should contain the content for   the first text/plain body part of the message. The mailto URL is   primarily intended for generation of short text messages that are   actually the content of automatic processing (such as "subscribe"   messages for mailing lists), not general MIME bodies.   Within mailto URLs, the characters "?", "=", "&" are reserved.   Because the "&" (ampersand) character is reserved in HTML, any mailto   URL which contains an ampersand must be spelled differently in HTML   than in other contexts.  A mailto URL which appears in an HTML   document must use "&" instead of "&".   Also note that it is legal to specify both "to" and an "hname" whose   value is "to". That is,     mailto:addr1%2C%20addr2     is equivalent to     mailto:?to=addr1%2C%20addr2     is equivalent to     mailto:addr1?to=addr2   8-bit characters in mailto URLs are forbidden. MIME encoded words (as   defined in [RFC2047]) are permitted in header values, but not for any   part of a "body" hname.Hoffman, et. al.            Standards Track                     [Page 2]

RFC 2368                 The mailto URL scheme                 July 19983. Semantics and operations   A mailto URL designates an "internet resource", which is the mailbox   specified in the address. When additional headers are supplied, the   resource designated is the same address, but with an additional   profile for accessing the resource. While there are Internet   resources that can only be accessed via electronic mail, the mailto   URL is not intended as a way of retrieving such objects   automatically.   In current practice, resolving URLs such as those in the "http"   scheme causes an immediate interaction between client software and a   host running an interactive server. The "mailto" URL has unusual   semantics because resolving such a URL does not cause an immediate   interaction. Instead, the client creates a message to the designated   address with the various header fields set as default. The user can   edit the message, send this message unedited, or choose not to send   the message. The operation of how any URL scheme is resolved is not   mandated by the URL specifications.4. Unsafe headers   The user agent interpreting a mailto URL SHOULD choose not to create   a message if any of the headers are considered dangerous; it may also   choose to create a message with only a subset of the headers given in   the URL.  Only the Subject, Keywords, and Body headers are believed   to be both safe and useful.   The creator of a mailto URL cannot expect the resolver of a URL to   understand more than the "subject" and "body" headers. Clients that   resolve mailto URLs into mail messages should be able to correctly   createRFC 822-compliant mail messages using the "subject" and "body"   headers.5. EncodingRFC 1738 requires that many characters in URLs be encoded. This   affects the mailto scheme for some common characters that might   appear in addresses, headers or message contents. One such character   is space (" ", ASCII hex 20). Note the examples above that use "%20"   for space in the message body.  Also note that line breaks in the   body of a message MUST be encoded with "%0D%0A".   People creating mailto URLs must be careful to encode any reserved   characters that are used in the URLs so that properly-written URL   interpreters can read them. Also, client software that reads URLs   must be careful to decode strings before creating the mail message soHoffman, et. al.            Standards Track                     [Page 3]

RFC 2368                 The mailto URL scheme                 July 1998   that the mail messages appear in a form that the recipient will   understand. These strings should be decoded before showing the user   the message.   The mailto URL scheme is limited in that it does not provide for   substitution of variables. Thus, a message body that must include a   user's email address can not be encoded using the mailto URL. This   limitation also prevents mailto URLs that are signed with public keys   and other such variable information.6. Examples   URLs for an ordinary individual mailing address:     <mailto:chris@example.com>   A URL for a mail response system that requires the name of the file   in the subject:     <mailto:infobot@example.com?subject=current-issue>   A mail response system that requires a "send" request in the body:     <mailto:infobot@example.com?body=send%20current-issue>   A similar URL could have two lines with different "send" requests (in   this case, "send current-issue" and, on the next line, "send index".)     <mailto:infobot@example.com?body=send%20current-     issue%0D%0Asend%20index>   An interesting use of your mailto URL is when browsing archives of   messages. Each browsed message might contain a mailto URL like:     <mailto:foobar@example.com?In-Reply-     To=%3c3469A91.D10AF4C@example.com>   A request to subscribe to a mailing list:     <mailto:majordomo@example.com?body=subscribe%20bamboo-l>   A URL for a single user which includes a CC of another user:     <mailto:joe@example.com?cc=bob@example.com&body=hello>   Another way of expressing the same thing:     <mailto:?to=joe@example.com&cc=bob@example.com&body=hello>Hoffman, et. al.            Standards Track                     [Page 4]

RFC 2368                 The mailto URL scheme                 July 1998   Note the use of the "&" reserved character, above. The following   example, by using "?" twice, is incorrect:     <mailto:joe@example.com?cc=bob@example.com?body=hello>   ; WRONG!   According toRFC 822, the characters "?", "&", and even "%" may occur   in addr-specs. The fact that they are reserved characters in this URL   scheme is not a problem: those characters may appear in mailto URLs,   they just may not appear in unencoded form. The standard URL encoding   mechanisms ("%" followed by a two-digit hex number) must be used in   certain cases.   To indicate the address "gorby%kremvax@example.com" one would do:     <mailto:gorby%25kremvax@example.com>   To indicate the address "unlikely?address@example.com", and include   another header, one would do:     <mailto:unlikely%3Faddress@example.com?blat=foop>   As described above, the "&" (ampersand) character is reserved in HTML   and must be replacded with "&amp;". Thus, a complex URL that has   internal ampersands might look like:     Click     <a href="mailto:?to=joe@xyz.com&amp;cc=bob@xyz.com&amp;body=hello">     mailto:?to=joe@xyz.com&amp;cc=bob@xyz.com&amp;body=hello</a> to     send a greeting message to <i>Joe and Bob</i>.7. Security Considerations   The mailto scheme can be used to send a message from one user to   another, and thus can introduce many security concerns. Mail messages   can be logged at the originating site, the recipient site, and   intermediary sites along the delivery path. If the messages are not   encoded, they can also be read at any of those sites.   A mailto URL gives a template for a message that can be sent by mail   client software. The contents of that template may be opaque or   difficult to read by the user at the time of specifying the URL.   Thus, a mail client should never send a message based on a mailto URL   without first showing the user the full message that will be sent   (including all headers that were specified by the mailto URL), fully   decoded, and asking the user for approval to send the message as   electronic mail. The mail client should also make it clear that the   user is about to send an electronic mail message, since the user may   not be aware that this is the result of a mailto URL.Hoffman, et. al.            Standards Track                     [Page 5]

RFC 2368                 The mailto URL scheme                 July 1998   A mail client should never send anything without complete disclosure   to the user of what is will be sent; it should disclose not only the   message destination, but also any headers. Unrecognized headers, or   headers with values inconsistent with those the mail client would   normally send should be especially suspect. MIME headers (MIME-   Version, Content-*) are most likely inappropriate, as are those   relating to routing (From, Bcc, Apparently-To, etc.)   Note that some headers are inherently unsafe to include in a message   generated from a URL. For example, headers such as "From:", "Bcc:",   and so on, should never be interpreted from a URL. In general, the   fewer headers interpreted from the URL, the less likely it is that a   sending agent will create an unsafe message.   Examples of problems with sending unapproved mail include:     * mail that breaks laws upon delivery, such as making illegal       threats;     * mail that identifies the sender as someone interested in breaking       laws;     * mail that identifies the sender to an unwanted third party;     * mail that causes a financial charge to be incurred on the sender;     * mail that causes an action on the recipient machine that causes       damage that might be attributed to the sender.   Programs that interpret mailto URLs should ensure that the SMTP   "From" address is set and correct.8. IANA Considerations   This document changes the definition of the mailto: URI scheme; any   registry of URI schemes should refer to this document rather than its   predecessor,RFC 1738.Hoffman, et. al.            Standards Track                     [Page 6]

RFC 2368                 The mailto URL scheme                 July 19989. References   [RFC822] Crocker, D., "Standard for the Format of ARPA Internet Text            Messages", STD 11,RFC 822, August 1982.   [RFC1738] Berners-Lee, T., Masinter, L., and M. McCahill, Editors,             "Uniform Resource Locators (URL)",RFC 1738, December 1994.   [RFC1808] Fielding, R., "Relative Uniform Resource Locators",RFC1808, June 1995.   [RFC2047] Moore, K., "MIME Part Three: Message Header Extensions for             Non-ASCII Text",RFC 2047, November 1996.Hoffman, et. al.            Standards Track                     [Page 7]

RFC 2368                 The mailto URL scheme                 July 1998A. Change fromRFC 1738RFC 1738 defined only a simple 'mailto' with no headers, just an   addr-spec (not a full mailbox.)  However, required usage and   implementation has led to the development of an extended syntax that   included more header fields.B. Acknowledgments   This document was derived fromRFC 1738 andRFC 1808 [RFC1808]; the   acknowledgments from those specifications still applies.   The following people contributed to this memo or had and discussed   similar ideas for mailto.   Harald Alvestrand   Bryan Costales   Steve Dorner   Al Gilman   Mark Joseph   Laurence Lundblade   Keith Moore   Jacob Palme   Michael PattonHoffman, et. al.            Standards Track                     [Page 8]

RFC 2368                 The mailto URL scheme                 July 1998C. Author Contact Information   Paul E. Hoffman   Internet Mail Consortium   127 Segre Place   Santa Cruz, CA  95060 USA   EMail: phoffman@imc.org   Larry Masinter   Xerox Corporation   3333 Coyote Hill Road   Palo Alto, CA 94304 USA   EMail: masinter@parc.xerox.com   Jamie Zawinski   Netscape Communications Corp.   501 East Middlefield Road   Mountain View, CA 94043 USA   EMail: jwz@netscape.comHoffman, et. al.            Standards Track                     [Page 9]

RFC 2368                 The mailto URL scheme                 July 1998D.  Full Copyright Statement   Copyright (C) The Internet Society (1998).  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 implementation 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.   This document and the information contained herein is provided on an   "AS IS" basis and THE INTERNET SOCIETY AND THE INTERNET ENGINEERING   TASK FORCE DISCLAIMS ALL WARRANTIES, EXPRESS OR IMPLIED, INCLUDING   BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE INFORMATION   HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES OF   MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.Hoffman, et. al.            Standards Track                    [Page 10]