Subject: comp.mail.mime FAQ (frequently asked questions list)
Date: 8 Aug 1997 06:30:10 GMT
Summary: This posting contains answers to some of the Frequently Asked
    Questions about MIME (Multipurpose Internet Mail Extensions).
    Please read it before posting a question to comp.mail.mime.
    ** Correspondence to the MIME FAQ maintainer primarily should
    concern corrections, additions, or suggestions for improve-
    ments to the MIME FAQ. **
Xref: senator-bedfellow.mit.edu comp.mail.mime:10725 comp.answers:27510 news.answers:109393

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==========================================================
comp.mail.mime frequently asked questions list (FAQ) (1/9)
==========================================================
Part 1: Introductions and Basic Information about MIME
--

i) Overview

This is part 1 of a Frequently Asked Questions document about MIME,
the multipurpose and multi-media standard for Internet mail.

There are 9 parts, each posted separately.

--

ii) Contents

Sections in the table of contents that have changed since the last
posting are marked with a '!' in the first column.  New sections are
marked with '+'.

Part 1: Introductions and Basic Information about MIME

  i)       Overview
  ii)      Contents

  1.1)     What is MIME?
  1.2)     Help!  I got a message in MIME format--how do I decode it?
  1.3)     MIME glossary
  1.4)     Conventions used in this FAQ document
  1.5)     Where to find information about MIME
  1.6)     Where can I get the comp.mail.mime FAQ?
  1.7)     FAQ Maintainers
  1.8)     Acknowledgements
  1.9)     Permissions

Part 2: MIME End-User topics

  2.1)     What can I use to display MIME messages?
  2.2)     MIME features that may or may not be present
  2.3)     Why does MIME define base64 instead of using uuencode?
  2.4)     How can I use uuencode with MIME?
  2.5)     Does Microsoft Mail support MIME?
  2.6)     What do I do with binhex-ed mail?
  2.7)     Can I do MIME on a (pick one) PC/Macintosh/Envoy/Whatever?
  2.8)     MIME support in commercial mail services

Part 3: Advanced MIME topics

  3.1)     So, does MIME introduce any new security problems?
  
  3.2)     What about security and privacy issues?
  3.2.1)   PEM
  3.2.2)   MOSS
  3.2.3)   PGP
  3.2.4)   S/MIME
  
  3.3)     What's "text/enriched"?
  3.4)     What about a group 3 facsimile encoding?
  3.5)     Should I always use external body parts to save space?
  3.6)     What mail servers can I reference?
  3.7)     Can I interwork between MIME and X.400?
  3.8)     Where else is MIME used?
  3.9)     How can I register a new MIME type?
  3.10)    What's ESMTP, and how does it affect MIME?
  3.11)    Where can I get some sample MIME messages?
  3.12)    Wouldn't MIME be better if it did <foo>?
  3.13)    So what about multilevel encodings?
  3.14)    Why doesn't MIME include a mechanism for compression?
  3.15)    What's this Content-Disposition header?
  3.16)    What character sets can be used with MIME?

Part 4: Appendix A(1): Pointers to MIME specifications

! A)       Pointers to MIME specifications
! A.1)     MIME-relevant RFCs, drafts, and standards
  A.2)     MIME types
! A.2.1)   List of registered MIME types

Part 5: Appendix A(2): Pointers to MIME specifications (continued)

! A.2.1)   List of registered MIME types (continued)
! A.2.2)   List of known unregistered MIME types

Part 6: Appendix B(1): Freely Available MIME products

  B)       Freely Available MIME products
  B.1)     Libraries and Patches
! B.2)     Conversion tools and extension packages

Part 7: Appendix B(2): Freely Available MIME products (continued)

  B.3)     Mail user agents and transport systems
  B.4)     Packages for MIME in USENET

Part 8: Appendix C(1): Commercial MIME products

  C)       Commercial MIME products

Part 9: Appendix C(2): Commercial MIME products (continued)

  C)       Commercial MIME products (continued)

--


1.1) What is MIME?
  
MIME, the Multi-purpose Internet Mail Extensions, is a freely
available set of specifications that offers a way to interchange text
in languages with different character sets, and multi-media e-mail
among many different computer systems that use Internet mail
standards.

If you were bored with plain text e-mail messages, thanks to MIME you
now can create and read e-mail messages containing these things:

        - character sets other than US-ASCII
        - enriched text
        - images
        - sounds
        - other messages (reliably encapsulated)
        - tar files
        - PostScript
        - pointers to FTPable files
        - 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.

Before MIME became widespread, you might have been able to create a
message containing, say, a PostScript document and audio annotations,
but more often then not, the message was encoded in a proprietary,
non-transportable format.  That meant that you couldn't easily handle
the same message on another vendor's workstation, or even get it
intact through a mail gateway in the first place.  Now, depending on
the completeness of your MIME-capable mail system, there's a good
chance that it'll "just work" (but see section 1.2 for some warnings
on this subject).

One of the best things about MIME is that it's a "four-wheel drive
protocol" (to borrow a description applied originally to PhoneNet by
Einar Stefferud).  MIME was carefully designed to survive many of the
most bizarre variations of SMTP, UUCP, and other Procrustean mail
transport protocols that like to slice, dice, and stretch the headers
and bodies of e-mail messages.

Here are a few 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 e-mail 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/html" form (RFC 1866), suitable for 
          examination via a WWW browser. (Formerly,
          text/richtext, another SGML-like markup language,
          was used.)
  
          - in an ordinary, plain text, form.
  
     (SNMP is the Simple Network Management Protocol.)
  
  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 1.3 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.
  
  3. A "pointer" to this FAQ is posted weekly in comp.mail.mime.  The
     pointer article contains MIME external contents that MIME-capable
     mail user agents can use to obtain the FAQ via WWW, Internet FTP,
     or mail server.

--

1.2) Help!  I got a message in MIME format--how do I decode it?

If you receive some content type that your mail user agent can't
already handle automatically, then you'll have to modify your global
or personal mail system configuration to deal with it--if you can.
It's not always possible, short of spending a year of your life to
write the required programs.

Some bits of advice:

 - Look in the MIME FAQ (part 1 of which you're reading now) to
   see if someone already has a tool or product that will decode the
   content type that you're attempting to handle.  Appendices B and C
   list many MIME-capable products and packages, some commercial,
   some free.

 
 - Check the MIME Meta-FAQ.  It's posted in comp.mail.mime along
   with this FAQ.  The meta-FAQ offers general advice for dealing
   with various MIME problems.  The meta-FAQ also may be found at 
   this URL:
 
   ftp://ftp.ics.uci.edu/pub/mh/contrib/multimedia/mime-meta-FAQ
 
 
 - A common decoding question is about "base64".  Technically,
   base64 is a content transfer encoding, not a MIME type per se.
   It looks like line after line of evil stuff like this:
 
     H52QbdC0aJOmTZkXbcKkYUNGzhs4ACJKnEixosWLGDNq3FgRhEcbNG...
 
   To decode it, you need something that'll unpack base64.  One
   solution, called "munpack", may be found at this URL:
   
   ftp://ftp.andrew.cmu.edu/pub/mpack/
   
   Versions are available for Unix, MS-DOS, Macintosh, and Amiga
   platforms.  See the Meta-FAQ for some hints and tips about how
   to run munpack.  Other decoders, some free, some commercial,
   are listed in appendices B and C of this FAQ.

                        *       *       *

Here your faithful MIME FAQ maintainer feels the need to rant a bit on
the subject of poor MIME usage and concomitant MIME decoding problems.

MIME capability doesn't automatically confer interoperability with the
rest of the world.  Any random data can be mapped into MIME one way or
another, but some consideration needs to be given to the target
audiences.

Still, as Einar Stefferud likes to point out, "'Can' implies 'shall.'"
Platform or application-specific MIME data formats inevitably leak out
to the rest of the world, prompting instant FAQs: "Huh?  Now how do I
make my mail reader handle _this_?  And why was it sent to me?"

For creators of MIME messages, here are some preventive suggestions:


  - Know how your attachments are going to be sent.  Bear in mind
    that what's reasonable for another Macintosh/Windows/Envoy/Whatever
    recipient isn't necessarily reasonable for the rest of the world.
    For example, sending that Microsoft Word document as an attachment
    might not work out as well as you think it should.

    If options are available for turning off attachments, do so,
    except perhaps for specific correspondents known to have the
    ability to view the attachments.  This is particularly relevant to
    users of mail systems in Microsoft operating environments.

    Microsoft TNEF data, for example, which has been seen to be 
    leaking out to the wider Internet, is not something that most
    Internet correspondents can presently handle.  In addition to
    attachments, TNEF data may include links to OLE objects, fonts,
    colors, and other information that doesn't have the same form
    or meaning outside a Microsoft operating environment.


  - Be somewhat conservative about content types when sending to
    mailing lists or other public forums, or consider using
    multipart/alternative.


  - Watch character set selections and content transfer encodings.
    For example, some commonly used character sets on Apple Macintosh
    computers use eight bits, not the standard seven bits, and also
    contain a few non-standard glyphs.

    Here is an example of a typical issue for personal computer
    users:

        [ Michael P Urban <urban@cobra.jpl.nasa.gov> 14-Feb-1996 ]
    
        If you want to send non-ASCII text (e.g., if you are a
        Macintosh user and you send text containing a bullet), you
        should realize that the mail system has NO WAY of knowing
        whether the recipient has the same sort of computer you have.
        The non-ASCII binary code for a bullet on a Macintosh is
        different from the one used on Intel machines, which is
        different from LATIN-1 (which has no such character).

--

1.3) MIME glossary

Every subculture needs its list of buzzwords; here's a small
collection for MIME.
  
body            the part of a message after the header (the "meat")
content         a portion of a MIME message
CTE             content transfer encoding (e.g. base64, quoted-printable, etc.)
ESMTP           Extended SMTP - RFC 1869
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
HTML            hypertext markup language; used in WWW documents
JPEG            an image compression standard for still images
mail transport  the "post office", e.g. sendmail, smail, MMDF, etc.
MIME            Multipurpose Internet Mail Extensions - RFCs 2045-2049
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
PGP             Pretty Good Privacy
PostScript      a popular page description language
RFC             request for comments; proposed or standard Internet protocols
SMTP            Simple Mail Transfer Protocol - RFC 821
text/enriched   simple text markup language for MIME - RFC 1896
text/simplemail another (even simpler?) text markup language
URL             WWW uniform resource locator; access-method://host/path
user agent      the end user's mail program, e.g. MH, ELM, /bin/mail, etc.
WWW             the world-wide web

--

1.4) Conventions used in this FAQ document

 - Direct quotations begin with an attribution in a standard format,
   and are indented by four spaces.
 
 
 - Pointers to resources available via the Internet, such as references
   to FTPable goodies, appear in WWW URL format.  URLs beginning with
   "ftp:" refer to FTP sites.  For example:
 
   ftp://domain.name/path/to/package
 
   Those with FTP access, but without WWW access, may treat such
   references as follows:
 
   1. Log into host domain.name using anonymous FTP
   2. Look for /path/to/package
 
   An FTP reference usually lists only the distribution site; please
   try your nearest FTP archive first.  Archie may be of some help
   here.
 
   URLs beginning with "http:" refer to WWW servers.  URLs beginning
   with "gopher:" refer to gopher servers.
 
   Internet browsing tools, such as Mosaic, know about URLs.
 
 
 - You'll occasionally see text in braces, like this.
 
   { Here is some example meta-text. }
 
   Sometimes, this indicates a place where information is missing, or
   where the information may be unreliable, or where major changes are
   planned 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 send e-mail to the maintainer.

--

1.5) Where to find information about MIME

{ Please feel free to contribute references to books, articles,
  web pages, newsgroups, and other sources of information. }


Books:

   The Internet Message: closing the book with electronic mail
  
   Marshall T. Rose
   Prentice-Hall
   ISBN 0-13-092941-7
   
   This book 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.

 
Articles and Papers:

    [ Daniel Glazman <Daniel.Glazman@der.edf.fr> 27-Oct-94 ]

    (In English):

        N.Borenstein, Bellcore, "Multimedia Mail From the Bottom Up or
                Teaching Dumb Mailers to Sing", ConneXions, pp. 10-16, Nov.91

        G.Vaudreuil, CNRI, "MIME: Multi-Media, Multi-Lingual Extensions for
                RFC 822 Based Electronic Mail", ConneXions, pp. 36-39, Sep.92

    (In French):

        D.Glazman, EDF/DER, "Les Extensions MIME", Tribunix No 57, Oct.94


Information available from the Internet:

   - Via FTP:

   Information about FTPable stuff is scattered throughout this FAQ.
   More specifically, look into the RFCs mentioned in appendix A of
   this FAQ.
   
   Other goodies can be found in the MH and MetaMail source trees.  
   
   Refer to the appendices of this FAQ for lots of details and URLs
   beginning with "ftp:".

   Refer to appendix A for information about how to retrieve RFCs via
   FTP.


   A nice overview of the MIME specification by Mark Grand is available
   from this URL:
   
   http://www.mindspring.com/~mgrand/mime.html

   
   - Via Mail-based archive servers:

   A few Internet sites whose archives contain MIME-related information
   support retrieval via e-mail servers.  One of these is ics.uci.edu.
   References in URL form to ftp.ics.uci.edu may be used to formulate
   retrieval requests to send to the archive-server address at
   ics.uci.edu.  To find out more about how to use that mail server, send
   a message whose body contains the line "help" to the address
   "archive-server@ics.uci.edu".
   
   RFCs may be requested from a mail-based archive server.  Refer to
   appendix A for information about how to do that.
   
   Several freely available packages, including ServiceMail and metamail,
   contain mail-based archive servers.  Some commercial packages do as
   well.  Refer to appendices B and C of this FAQ for details.  Installing
   a mail-based archive server at your site makes it possible to send out
   messages containing external body contents that can be used to
   retrieve materials automatically from your site via e-mail.

       [ Arjan van der Meer <arjanvdm@htsa.hva.nl> 30-Jan-1995 ]
   
       Mail for more info: mime-DocServer@docserver.cac.washington.edu
       It sent me a brief and clear E-mailing about how and what MIME is.


   - From USENET newsgroups:

   news:comp.mail.mime

     This is the USENET newsgroup devoted to discussions of MIME.
   
     Comp.mail.mime articles are archived here:
  
          ftp://ftp.ncd.com/pub/usenet/comp.mail.mime 
  
     Articles are stored in three formats: by subject, by article
     number, and by month.  See the README file for more information.
 

   news:comp.mail.multi-media 

     This newsgroup contains general discussions of multi-media e-mail,
     not necessarily MIME.
 
 
   - From Internet mailing lists:

   info-mime

     Info-mime is gatewayed with comp.mail.mime.  This is a
     bidirectional gateway, so every message to the mailing list also
     appears on the newsgroup, and vice versa.  If you are unable or
     unwilling to read USENET news, here is where to send subscription
     requests:
 
         info-mime-request@cs.utk.edu
 

   info-mime-uk

     This is a UK exploder for info-mime.  Here is where to send
     subscription requests:
 
         info-mime-uk-request@mailbase.ac.uk
 
     Mailbase software archives all articles sent to the info-mime-uk
     mailing list.  The articles are accessible via these URLs:
   
     ftp://mailbase.ac.uk
     gopher://mailbase.ac.uk
   
     Archived articles are also available via mailserver; send a message
     to mailbase@mailbase.ac.uk, with a message body containing a
     retrieval command, e.g. "send info-mime-uk 08-1993".


   ietf-types

     RFC 2048 makes mention of a discussion list for proposed MIME type
     registration, "ietf-types".  The subscription address is this:

        majordomo@aun.uninett.no

     In the body of the request message specify this command:

        subscribe ietf-types your-address@your_site.your_net

     Please see also section 3.9 of this FAQ for some additional notes
     about making proposed MIME type registrations available for
     review on the ietf-types list.


   other lists

     There are various mailing lists specific to particular
     implementations of MIME.  If we know of such a list, it is
     mentioned in the section of this document about that
     implementation.


   - From the world-wide web:

   There are many web URLs scattered throughout this document.
   Various sources of information about mail systems that support
   MIME may also be found at these URLs (list contributed by
   Brad Knowles <brad@azathoth.ops.aol.com>):

   Internet Mail Consortium
     http://www.imc.org/

   Brad Knowles's comp.mail.sendmail FAQ
     http://www.his.com/~brad/sendmail/

   SMTP Resources Directory
     http://www.dns.net/smtprd/

   SunWorld Online Email Connectivity overview
     http://www.sun.com/sunworldonline/swol-08-1995/swol-08-connectivity.html

   Matt Wall's E-mail Web Resources
     http://andrew2.andrew.cmu.edu/cyrus/email/email.html

   Bill Wohler's Email References
     http://www.worldtalk.com/html/msg_resources/email_ref.html

--

1.6) 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 that honor this field---the most recent edition
   shall always be in the news article database.
 
 
 - Many sites archive news.answers postings, including these:
   
   ftp://ftp.uu.net/usenet/news.answers/mail/mime-faq/
   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".  Alternatively, use WWW search
   engines to look for the MIME FAQ.
   
 
 - An HTML version of the MIME FAQ is available at this URL:
 
   http://www.cs.ruu.nl/wais/html/na-dir/mail/mime-faq/.html
        (Brought to you by the Department of Computer Science, 
         Utrecht University, The Netherlands.)
 
   If you find a non-working hypertext link in the HTML versions,
   you're welcome to bring it to the attention of the MIME FAQ
   maintainer, but unless it's a problem with a URL reference in the
   original document, the MIME FAQ maintainer probably can't fix it
   directly.

 
 - 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.


There is also a Part 0, the "Meta-FAQ", posted monthly, that attempts
to help with any special problems that you may have with reading MIME
messages such as the MIME FAQ postings.  A pointer to the Meta-FAQ
is posted weekly.  The Meta-FAQ is usually available with the MIME FAQ;
look for "comp.mail.mime meta-FAQ: Help for MIME problems".  The 
meta-FAQ's filename is typically "mime0".

--

1.7) FAQ Maintainers

Current maintainer:
  Jerry Sweet <mime-faq@ics.uci.edu>

    Please note:
  
    Questions about mail systems, how to decode MIME parts on your
    computer, and other such issues, if not already answered in the
    FAQ, should be posted to comp.mail.mime or to the info-mime mailing
    list.

    Correspondence sent to the MIME FAQ maintainer primarily should 
    address information in the MIME FAQ---corrections, additions, or
    suggestions for improvement.  You must put the word "maint:"
    at the beginning of your subject, or you'll get an automated
    response.
  
Previous maintainers (thanks, guys!):
  Ed Vielmetti - originator
  Tim Goodwin

Contributions have come from a cast of dozens; see below for the
list of contributors.

--

1.8) Acknowledgements

In addition to those named elsewhere in this document, contributors to
this document have included these persons:

Niklas Agren
Harald Alvestrand
Ed Anselmo
Ran Atkinson
Ron Barak
David Barr
Jason Beyer
Axel Boldt
Nathaniel Borenstein
Yehavi Bourvine
Douglas Boyce
David Collier-Brown
Mark Crispin
Dave Curry
Roman Czyborra
Christopher Davis
Steve Dorner
David Eaves
Paul Eggert
Daniel Fandrich
Pat Farrell
James Ford
Ned Freed
John Gardiner Myers
Daniel Glazman
Tim Goodwin
Mark Grand
Ed Greshko
Joergen Haegg
Gisle Hannemyr
Alec Henderson
Steve Hole
Ian Hoyle
Craig Huckabee
Joe Ilacqua
Olle Jarnefors
Tim Kehres
Brad Knowles
Dave Lacey
Ray Langford
Carlyn Lowery
Stuart Lynne
John Martin
David Miller
Keith Moore
Lars-Gunnar Olsson
Michael Parson
Jerry Peek
Chris Pepper
John R MacMillan
Rich Ragan
Joyce Reynolds
Alan Robiette
John Romine
Luc Rooijakkers
Marshall Rose
Remco Rutten
Larry Salomon Jr
Rahmat M. Samik-Ibrahim
Piero Serini
Michael Shields
Quentin Smart
Susan Straub
Jerry Sweet
Rick Troth
Masanobu Umeda
Michael Urban
Erik van der Poel
Marc VanHeyningen
Edward Vielmetti
Larry W. Virden
Tommy Wallo
Jay Weber
Syd Weinstein
Martin Wendel
Alan Wehmann
Sascha Wildner
Christophe Wolfhugel

If we've left your name off please accept our apologies.  Drop us a
note and we'll include it for next time.

The following institutions and individuals have provided resources for
maintaining the MIME FAQ:

- The University of California, Irvine; Department of Information and 
    Computer Science (http://www.ics.uci.edu)
- Einar Stefferud <stef@nma.com>
- Irvine Compiler Corp (http://www.irvine.com)

Thanks also go to Jonathan Kamens, for coordinating the *.answers
groups, and for his post_faq program which brought you this FAQ.

--

1.9) Permissions

Permission is granted for non-profit redistribution of the unedited
comp.mail.mime FAQ.

For-profit redistribution of the unedited comp.mail.mime FAQ is
presently permitted, but the maintainers request that you notify them.
(For this purpose, commercial USENET newsfeeds, bboards, and other
electronic or physical media distributions that incidentally include
this FAQ as part of a full re-distribution of the newsgroups in which
the FAQ appears, needn't notify us.)

--

End of Part 1
*************
--
