home *** CD-ROM | disk | FTP | other *** search
- Archive-Name: mail/mime-faq/part1
- Last-modified: 1994/02/10
- Version: 3.4
- Message-ID: <mime_764279514@pipex.net>
- MIME-Version: 1.0
- Content-Type: text/plain; charset=us-ascii
- Content-Transfer-Encoding: 7bit
-
-
- comp.mail.mime frequently asked questions list (FAQ) (1/3)
-
- Part I -- Frequently Asked Questions
-
- This is part I of a Frequently Asked Questions document about MIME, the
- multipurpose and multi-media standard for Internet mail.
-
- Part I covers frequently asked questions.
-
- Part II is a listing of MIME products.
-
- Part III covers advanced topics.
-
-
- 0 Contents
-
- Sections which have changed since the last posting are marked with a `!' in
- the first column. New sections are marked with `+'.
-
- Part I -- Frequently Asked Questions
-
- 0 Contents
-
- 1 Introduction
- 1.1 Authorship
- 1.2 Conventions
- + 1.3 Where can I get the comp.mail.mime FAQ?
-
- 2 What is MIME?
- 2.1 Introduction
- 2.2 MIME features that may or may not be present
- 2.3 Further information
- 2.4 MIME glossary
- 2.5 Newsgroups and mailing lists
-
- 3 Miscellaneous questions
- 3.1 What can I use to display MIME messages?
- 3.2 What's "text/enriched"? "text/simplemail"?
- 3.3 What about security issues?
- 3.4 So, does MIME introduce any new security problems?
- 3.5 What about a group 3 facsimile encoding?
- 3.6 Should I always use external body parts to save space?
- 3.7 What mail servers can I reference?
- 3.8 Can I interwork between MIME and X.400?
- 3.9 How can I use uuencode with MIME?
-
- 4 MIME information available from the Internet
- 4.1 Anonymous FTP
- 4.2 Mail based archive servers
- 4.2.1 Eitech "ServiceMail"
- 4.2.2 Metamail "mailserver"
- 4.3 Gopher
- 4.4 World Wide Web
-
- ! 5 Published books and articles
-
- 6 MIME based relays for commercial mail services
- 6.1 Large national or international providers
- 6.1.1 ATTMAIL
- + 6.1.2 CompuServ
- 6.1.3 Radiomail
- 6.2 Local and regional providers
-
-
- Part II -- MIME products
-
- ! 7 Freely available MIME packages
- 7.1 Conversions from other mail systems
-
- ! 8 Commercial MIME packages
-
- 9 Packages for MIME in Usenet
- 9.1 Introduction
- 9.2 News readers and transports with MIME support
-
- Part III -- Advanced topics
-
- 10 Information
- 10.1 MIME-relevant RFCs and other standards
- 10.2 List of registered MIME types
- 10.3 Internet Engineering Task Force (IETF) working groups
-
- 11 Developers' FAQs
- 11.1 How can I register a new MIME type?
- 11.2 What's ESMTP, and how does it affect MIME?
- 11.3 Where can I get some sample MIME messages?
- 11.4 Wouldn't MIME be better if it did <foo>?
- 11.5 So what about multilevel encodings?
- 11.6 Why doesn't MIME include a mechanism for compression?
-
- ! 12 Acknowledgements
-
-
- 1 Introduction
-
- 1.1 Authorship
-
- This FAQ was begun by Ed Vielmetti. It is now maintained by me, Tim
- Goodwin. Contributions have come from a cast of dozens: see section 12
- for a list of contributors.
-
-
- 1.2 Conventions
-
- I have used some typographical conventions. Eventually I hope to format
- this as simplemail, but in the meantime...
-
- Direct quotations begin with an attribution in a standard format, and
- are indented by four spaces.
-
- FTPable goodies appear thus:
-
- FTP: domain.name:path/to/package
-
- Note that I usually list only the distribution site -- please try your
- nearest FTP archive first.
-
- You'll occasionally see text in braces, like this.
-
- { Here is some example meta-text. }
-
- Generally, these indicate places where information is missing, I'm
- unsure of my ground, or I plan major changes in the near future.
-
- You can ignore these if you're just looking for information. But if you
- can help fill in the gaps, and you want to achieve fame, fortune, and
- your name at the bottom of this FAQ, please mail me.
-
-
- 1.3 Where can I get the comp.mail.mime FAQ?
-
- It is posted approximately monthly to the newsgroups comp.mail.mime,
- comp.answers, and news.answers. The `Expires:' field is set such
- that---on systems which honour this field---the most recent edition
- will always be in the news spool.
-
- Many sites archive news.answers postings, including
-
- FTP: rtfm.mit.edu:pub/usenet-by-group/news.answers/mail/mime-faq/*
-
- If possible, please try to find a closer site; for example, by asking
- archie for `mime-faq'.
-
- If you are reading this FAQ via some fixed medium such as hardcopy or
- CD-ROM, please try to obtain the latest edition from the net instead.
-
-
- 2 What is MIME?
-
- 2.1 Introduction
-
- MIME, the Multi-purpose Internet Mail Extensions, is a freely available
- specification that offers a way to interchange text in languages with
- different character sets, and multi-media email among many different
- computer systems that use Internet mail standards.
-
- If you were bored with plain text email messages, thanks to MIME you
- now can create and read email messages containing these things:
-
- - character sets other than ASCII
- - enriched text
- - images
- - sounds
- - other messages (reliably encapsulated)
- - tar files
- - PostScript
- - FTPable file pointers
- - other stuff
-
- MIME supports not only several pre-defined types of non-textual
- message contents, such as 8-bit 8000Hz-sampled mu-LAW audio, GIF image
- files, and PostScript programs, but also permits you to define your
- own types of message parts.
-
- The ability to create email messages with audio and other non-textual
- contents has been around for a while, but almost always as part of a
- vendor-specific ``solution.'' This means that you can't create a
- message on a NeXT system containing PostScript information and ``Lip
- Service'' (NeXT's audio email tool) and easily handle the same
- message on an HP 9000/710, a Sun SPARCstation IPC, and a Silicon
- Graphics Iris. That's a problem that MIME helps to solve.
-
- One of the best things about MIME is that it's a "four-wheel drive
- protocol", to borrow a description of PhoneNet from Einar Stefferud.
- MIME was carefully designed to survive many of the most bizarre
- variations of SMTP, UUCP, and Procrustean mail transport protocols,
- such as BITNET and MMDF, that like to slice, dice, and stretch the
- headers and bodies of email messages.
-
- Here are a couple of examples of how MIME is being used in the real
- world, now.
-
- 1) Dr Marshall T. Rose mails out his SNMP-related newsletter, ``The
- Simple Times'' as multi-media email messages in several forms:
-
- - in a PostScript form, with beautiful typesetting and a
- two-column page layout, suitable for printing on a laser
- printer;
-
- - in a ``text/enriched'' form (explained in question 3.2), suitable
- for display on a mildly intelligent ASCII terminal; and
-
- - in a plain text, ordinary message form.
-
- (SNMP is the Simple Network Management Protocol, a low-level network
- management facility.)
-
- 2) IETF document announcements (RFCs, Internet Drafts, etc.) are
- structured as multipart MIME messages. The first part contains the
- document abstract. The second part is itself a multipart message,
- containing external references to the document itself (one via a
- mail-server, one via anonymous FTP). Thus, with a suitable UA (User
- Agent, see 2.4 for glossary), you can read the abstract, and then have
- the complete document retrieved for you (by the most appropriate method)
- at the press of a button.
-
-
- 2.2 MIME features that may or may not be present
-
- Implementations of multi-media email need not support the full spec;
- it's possible to have a useful product that does not explore all of
- the nooks and crannies of the standard.
-
- Furthermore, MIME permits a message to contain alternative parts for
- consumption by sites that can't necessarily display or listen to all
- the good stuff.
-
- Here is a list of features that someone with a good, functional
- mail user agent might include for MIME support.
-
- - Displays GIF, JPEG, and PBM encoded images, using e.g. 'xv' in the X
- Window System, or (name of windows program here) in Microsoft Windows.
-
- - Displays PostScript parts, using e.g. something that prints to a
- PostScript printer, or that invokes GhostScript on an X Window System
- display, or that uses Display PostScript.
-
- - Obtains external body parts via Internet FTP or via mail server.
-
- - Plays audio parts on workstations that support digital audio.
-
- On the other hand, the minimal requirements for a MIME-conformant MUA
- are almost trivial, yet still provide increased functionality. (The
- minimal requirements are mainly concerned with ensuring that users are
- not shown raw data from a MIME message inappropriately.)
-
-
- 2.3 Further information
-
- FTP: ftp.netcom.com:pub/mdg/mime.ps
- FTP: ftp.netcom.com:pub/mdg/mime.txt
-
- This is a nice overview of the MIME specification by Mark Grand.
-
- { Any other documents that should be referenced? }
-
-
- 2.4 MIME glossary
-
- Every subculture needs its list of buzzwords, here's a start at a
- collection for MIME.
-
- body the part of a message after the header (the "meat")
- ESMTP Extended SMTP - RFC 1425
- external part a "pointer" to a part available via FTP or other means.
- GIF graphical interchange format for images
- header the To, From, Subject, etc. at the start of a message
- JPEG an image compression standard for still images
- mail transport the "post office", e.g. sendmail, smail, MMDF, etc.
- MIME Multipurpose Internet Mail Extensions - RFC 1521
- MPEG an image compression standard for moving pictures
- MTA Mail Transport Agent, see "mail transport"
- MUA Mail User Agent, see "user agent"
- multi-media nebulous marketroid term meaning audio and visual stuff
- part a piece of a MIME message containing some data type
- PBM an image format
- PEM Privacy Enhanced Mail
- PostScript a popular page description language
- RFC request for comments; proposed or standard Internet protocols
- SMTP Simple Mail Transport Protocol - RFC 821
- text/enriched simple text markup language for MIME - RFC 1523
- text/simplemail another (even simpler?) text markup language
- user agent the end user's mail program, e.g. MH, ELM, /bin/mail, etc.
-
-
- 2.5 Newsgroups and mailing lists
-
- You're probably reading comp.mail.mime at the moment. There is a
- mailing list which is gatewayed with comp.mail.mime. If you are
- unable or unwilling to read Usenet news, send subscription requests to:
-
- info-mime-request@thumper.bellcore.com
-
- There is a UK exploder for info-mime, contact:
-
- info-mime-uk-request@mailbase.ac.uk
-
- The Mailbase software archives all contributions, which are then
- accessible via FTP and gopher (mailbase.ac.uk), and mailserver
- (mailbase@mailbase.ac.uk, with message body containing, e.g. "send
- info-mime-uk 08-1993"
-
- There is also a [comp.mail.multi-media] newsgroup, which contains
- general discussions of multi-media email, not necessarily MIME.
-
- There are various mailing lists specific to particular implementations
- of MIME. If I know of such a list, it is mentioned in the section on
- that implementation.
-
-
- 3 Miscellaneous questions
-
- 3.1 What can I use to display MIME messages?
-
- You need something that understands MIME-structured messages and also
- understands how to display the different kinds of body parts.
-
- Details of many freely available and commercial packages to do just
- that can be found in part II of this FAQ.
-
-
- 3.2 What's "text/enriched"? "text/simplemail"?
-
- These two subtypes of the "text" type have a similar aim: to offer
- simple text markup, without making the text unreadable to someone
- without the software to interpret it.
-
- The text/enriched scheme uses markup commands enclosed in angle
- brackets. For example, here is how you would <bold>embolden</bold> a
- single word.
-
- Simplemail is more like a standardisation of certain existing practices
- in mail and news articles. For example, here is how you would
- *emphasize* a single word.
-
- The text/enriched type is defined in RFC 1523. It supersedes
- "text/richtext", which was defined in RFC 1341.
-
-
- 3.3 What about security issues?
-
- Both users and administrators should be aware that ordinary Internet
- and UUCP email is not secure. No authentication, confidentiality, or
- data integrity properties are provided in SMTP, RFC-822, or MIME.
- People desiring any or all of those security properties in their email
- should look into the use of Privacy-Enhanced Mail (PEM). At least one
- no-cost implementation of PEM is available in the US and Canada.
- There are also a number of implementations being developed in Europe
- (hopefully these will not suffer the same restrictions on export).
-
- PEM will (eventually) be integrated with MIME. See
-
- draft-ietf-pem-mime-03.txt
-
- for the latest work on this.
-
- A system providing similar functionality to PEM implementations is
- PGP. PGP is an implementation, not a specification, and it does not
- carry the blessing of the IETF, or any other body. It is, however,
- available at no cost throughout the world (although its status with
- respect to certain US patents is dubious). Caveat emptor.
-
-
- 3.4 So, does MIME introduce any new security problems?
-
- Yes. MIME user agents can do previously unheard of things with mail
- messages, notably giving them as input to other programs.
-
- PostScript is probably the biggest potential security hole. One
- famous example is the "melting screen" PostScript program, which
- destroys screens maintained by Display PostScript implementations. For
- another example, PostScript can be used to change the password on some
- PostScript printers with previously undefined passwords, which denies
- the use of the printer until the printer's password can (somehow) be
- changed back. Yet other Display PostScript implementations may allow
- file operations. (NeXTstep wisely disables file operations. With
- GhostScript, they can be disabled by the "-dSAFER" command line option.
- Use of this option (in mailcap, etc.) is highly recommended.)
-
- The enumeration of these security holes is not to be interpreted as
- encouragement to exploit the holes. They are mentioned only because
- they are well known. Refer to books such as "Practical UNIX Security"
- and to news groups such as comp.security.misc for general information
- about system security.
-
-
- 3.5 What about a group 3 facsimile encoding?
-
- { This section needs some work - any volunteers? }
-
- It is rumored that there was an attempt to include G3 FAX in the
- current MIME standard, but that it was impossible for the authors of
- the MIME specification to gain a consensus on how to encode the data.
- So G3 FAX has been left for a future MIME implementation. But you can
- always define your own body part.
-
- Here are some snippets relevant to MIME and FAX.
-
- The MIME-MHS documents define a G3Fax body part that is conformant with
- the X.400 G3Fax definition.
-
- [ Stuart Lynne <sl@wimsey.com> 30-Dec-1992 ]
-
- I have prototype scripts operating with metamail to do some of this.
- Some of it is in contrib directory.
-
- Currently I have 2 scripts:
-
- mm2fax - convert mail and metamail messages to TIFF/F (uses various
- tools to convert different body parts to TIFF/F);
-
- faxmm - send rfc822 and mime email messages via facsimile (uses
- mm2fax to convert to TIFF/F).
-
- [ Ned Freed <ned@innosoft.com> 31-Dec-1992 ]
-
- PMDF-FAX is a set of channel programs for PMDF that provide
- facilities for converting text, PostScript, and various other
- formats into Group 3 FAX, as well as a set of programs that take
- these Group 3 FAX files and use them to drive a variety of FAX
- modems. MIME is used throughout to provide type information,
- multipart facilities, and so forth. PMDF-FAX was developed with MIME
- in mind from the outset.
-
-
- 3.6 Should I always use external body parts to save space?
-
- Not necessarily. In many cases, for example, at the ends of UUCP
- connections, your recipients may not be able to retrieve external body
- parts easily. It depends on your audience. Making files available via
- a mail server is to be encouraged. It is always possible to provide
- MIME alternative parts that first offer FTP, then mail server options.
-
-
- 3.7 What mail servers can I reference?
-
- There are various mail servers available. Check news.answers for
- the FAQ about mail server software. We do not presently have a
- recommendation.
-
-
- 3.8 Can I interwork between MIME and X.400?
-
- Conversion between RFC 822 and X.400 was defined in RFC 1327.
-
- Recently, the MIME-MHS working group has published RFCs (which are on
- the IAB standards track) which extend RFC 1327 to define conversions
- between MIME and X.400.
-
- { Sorry this is a bit scant---I haven't even had a chance to read the }
- { RFCs yet. Any contributions to this section gratefully received. }
-
-
- 3.9 How can I use uuencode with MIME?
-
- The following idea from Nathaniel may be useful. For some examples of
- this in action, see the newsgroup clari.feature.dilbert.
-
- [ Nathaniel Borenstein <nsb@thumper.bellcore.com> 4-Nov-93 ]
-
- I recently convinced myself that you can use multipart/alternative
- to get a nice effect for both MIME-smart recipients and
- uuencode-loving recipients, although it is ugly and wasteful:
-
- Content-type: multipart/alternative; boundary=foo
-
- --foo
- Content-type: application/octet-stream; name=foo.uu
-
- ...uuencoded data goes here....
- --foo
- Content-type: real-mime-type
- Content-type: base64
-
- base64-encoded data goes here
- --foo--
-
- A good MIME viewer will only use the second part, the real MIME
- data. A uuencode-oriented system, however, should ignore everything
- EXCEPT the uuencoded data, because of the way uuencode works
- (everything before the "begin" line and after the "end" line is
- ignored).
-
- I certainly wouldn't want to recommend the above as standard
- practice, but I imagine that are enclaves or situations where it
- could be useful.
-
-
- 4 MIME information available from the Internet
-
- 4.1 Anonymous FTP
-
- Information about FTPable stuff is scattered throughout this FAQ.
- More specifically, look into the RFCs, mentioned in item 2.4. Other
- goodies can be found in the MH and MetaMail source trees.
-
- FTP: thumper.bellcore.com:pub/nsb
-
- contains a collection of MIME sample messages which can be used to
- test implementations.
-
-
- 4.2 Mail based archive servers
-
- 4.2.1 Eitech "ServiceMail"
-
- [ Jay C. Weber <weber@eitech.COM> 13-Oct-1992 ]
-
- We (Enterprise Integration Technologies Corporation) have a MIME
- implementation, which we are distributing freely. Instead of a
- MIME MUA, it is a toolkit for building services that automatically
- process MIME messages. It is similar, in spirit, to the few other
- email-scripting packages except:
-
- o it exploits several MIME features
- o it is intended to run standalone (as opposed to a back-end to a MUA)
- o it uses TCL (from Berkeley) as its scripting language
-
- and support for PEM is in the works.
-
- EIT is providing ServiceMail access to the ServiceMail toolkit.
- If you have the METAMAIL or some other MIME-compliant mail reader,
- just send the message
-
- To: services@eitech.com
- Subject: archive-request servicemail.tar.Z
-
- and read the response(s) using METAMAIL. Save the result in
- servicemail.tar.Z
-
- The package can also be retrieved by anonymous FTP from the site
- eitech.com.
-
- If you have any problems with acquisition, installation, or use,
- don't hesitate to send mail to "servicemail-help@eitech.com" and
- ask for help.
-
- IF YOU WANT FUTURE UPDATES ON TOOL KIT VERSIONS, BUGS, AND
- SERVICES, MAKE SURE YOU ARE ON THE PACT-KIT MAILING LIST. To get
- on it, send a message to "services@eitech.com" with subject
- "listserv subscribe pact-kit your-real-name".
-
-
- 4.2.2 Metamail "mailserver"
-
- [ Nathaniel Borenstein <nsb@thumper.bellcore.com> 9-Jan-1993 ]
-
- The metamail distribution includes a simple "mailserver" shell
- script that can be used to operate a MIME-conformant mail server
- mechanism, e.g. for making anon-ftp files available as MIME mail.
- ServiceMail is also now available under the "contrib" area of the
- metamail distribution.
-
-
- 4.3 Gopher
-
- [ Randall Atkinson <atkinson@tengwar.itd.nrl.navy.mil> 2-Jan-1993 ]
-
- There is experimental work underway in the Internet Gopher community
- to include MIME as a mechanism for marking the content of files.
- The freely distributable Gopher client for NeXTstep 3.0 includes
- MIME support. Other gopher clients will probably add it eventually.
-
-
- 4.4 World Wide Web
-
- [ Marc VanHeyningen <mvanheyn@cs.indiana.edu> 26-Jun-1993 ]
-
- There is more-than-experimental work underway in the Internet World
- Wide Web (WWW) community to use MIME as the mechanism for marking
- the contents of information exchanged via HyperText Transfer
- Protocol (HTTP); the specification of HTTP/1.0 dictates that both
- the request and the response are more or less MIME-compliant
- messages. There are implementations already doing this today.
-
- Support is also included for format negotiation (e.g. a server
- might have both a PostScript and a plaintext version of a paper
- and decide which to send based on what the client can accept,
- presentation preferences, size, and the like.) It's nearly as
- complicated as the "badness" mechanisms in TeX, and unrelated to
- (and, for its application, probably superior to) the
- multipart/alternative MIME type.
-
- There is an FAQ for WWW in comp.infosystems.www
-
-
- 5 Published books and articles
-
- Published books or articles that cover MIME.
-
- Marshall T. Rose has recently published the fourth book in his
- networking `trilogy'.
-
- Marshall T. Rose
- "The Internet Message: closing the book with electronic mail"
- Prentice-Hall
- ISBN 0-13-092941-7
-
- It is a complete review of the Internet world of electronic mail,
- including recent developments. There is considerable detail, and it
- would make the perfect companion to the mail RFCs for any budding
- implementor.
-
- On the other hand, the detail should be quite easy to skip for those
- interested in just an overview.
-
- As usual, Marshall's informed and often vigorous opinions are clearly
- marked off as `soapboxes', to be objectively skipped or delightedly
- sought out, according to preference.
-
- One chapter of the book is devoted to MIME.
-
-
- [ Alec Henderson <alech@hpindda.cup.hp.com> 18-Dec-1992 ]
-
- There is a good introductory article on MIME in the September 1992
- issue of Connexions; also several other interesting articles on
- email, both MIME and X.400. (Ole Jacobsen, the Connexions
- editor, was kind enough to send me a copy of the September issue.)
-
-
- [ Daniel Glazman <Daniel.Glazman@grif.grif.fr> 30-Aug-1993 ]
-
- To be published soon in "TRIBUNIX" the French Unix Users Group
- (AFUU) newspaper: "Les extensions MIME", Daniel Glazman.
-
-
- 6 MIME based relays for commercial mail services
-
- 6.1 Large national or international providers
-
- { Lots missing here. Anyone got any info these, or any others? }
- { America On-line }
- { Dialog }
- { Genie }
- { MCI Mail }
- { Sprintmail }
-
-
- 6.1.1 ATTMAIL
-
- [ Steve <atthelp@attmail.com> 30-Dec-1992 ]
-
- We do support binary attachment but are not MIME compliant nor do
- we have an X.400 to MIME conversion header routine. This is 'in the
- works', however, and due to overwhelming interest by our users and
- other prmd's, research and development are currently engaged in
- working on the issue. I do not have any information on when this
- will be available, but will let you know when I receive word of our
- MIME status.
-
-
- 6.1.2 CompuServ
-
- [ Pat Farrell <pfarrell@netcom.com> 31-Dec-1993 ]
-
- CompuServ's main mail service is ASCII text based, and is not MIME
- compliant. CompuServ provides robust, reliable mail transport of
- binary files. CompuServ invented and copyrighted the GIF format
- which is supported by MIME. There are commercial and freeware client
- programs for Macs and PCs that can provide "user friendly" access
- to CompuServ's text and binary mail services, display GIF files,
- and interact with CompuServ's forums. (CompuServ forums are roughly
- equivalent to UseNet newsfeeds.)
-
-
- 6.1.3 Radiomail
-
- [ Jerry Sweet <jsweet@irvine.com> 17-Dec-1992 ]
-
- RadioMail Corp. (formerly Anterior Technology) operates three types
- of email services having these statuses with respect to MIME:
-
- 1. UUCP/Internet gatewaying. The gateway passes MIME messages using
- 7 bit encodings in either direction. The sender and receiver must,
- of course, have MIME-complaint user agents in order to handle MIME
- email.
-
- 2. cc:Mail/Internet gatewaying. cc:Mail does permit binary
- attachments of various types, and these attachments are encoded by
- the gateway for transfer via SMTP, but the encoding is not presently
- MIME compliant. This may change.
-
- 3. Wireless email gatewaying. This service can pass MIME messages
- using 7-bit encodings in either direction. However, MIME per se is
- understood neither by the MS-DOS hosted user agents presently
- supplied by RadioMail Corp. for use on radio modem equipped
- computers, nor by any RadioMail-compatible third-party MS-DOS
- hosted user agents. This may change.
-
- { Should coordinate this with the global email list that is posted to }
- { comp.mail.misc. }
-
-
- 6.2 Local and regional providers
-
- { Any info? Should coordinate this with e.g. the PDIAL list. }
-
-
- End of Part I
-