On Wed, 15 Feb 2012 15:46:49 -0500, Rich Greenberg <[log in to unmask]> wrote:

>Recently I added the ability to attach pictures to 2 dog lists.  As part
>of the announcement, I said that people on standard DIGEST would not see
>the attachments, 

Correct.  This was changed for 16.0.   
See  http://www.lsoft.com/news/techtipLSV-issue4-2011.asp

>they would have to go to DIGEST MIME or DIGEST HTML to
>see them.  Well, given the chance, of course some screwed it up.
>
>Questions for you and/or the Lsoft folks:
>
>1) If a DIGEST user has both MIME & HTML set, which do they get?

HTML DIGEST technically includes MIME DIGEST (see #3 below) so they get HTML
DIGEST (ie. HTML message content) unless the message was composed by original
author as plain-text only (i.e. before the message was sent to LISTSERV) OR
your list is set to

 Misc-Options= DISCARD_HTML (15.5 and later)
or
 Language= NOTHML  (15.0 and earlier)

which removes any HTML message parts leaving plain-text part only (but with
attachments, if any).  

>2) If someone not on DIGEST has either or both set, are they ignored?

Yes.  These settings apply only to the various forms of DIGEST or INDEX
subscription.

>3) Can somebody give me a short explanation of how MIME differs from
>   HTML.  

Let's see if I can do this at slightly less length than "War and Peace". ;-)

HTML email, in fact all modern email, requires and heavily uses MIME
(Multipurpose Internet Mail Extensions).  For technical details go to
http://www.rfc-editor.org/rfcsearch.html and type in MIME.  (I found 169
related standards, but RFC 2045 is a good starting point.)

Originally email was designed as 7-bit only, using the basic 128 ASCII
characters.  But very quickly people wanted to send more than simple plain
text.  It could be useful to send arbitrary binary data (images, spreadsheets,
word-processor documents, later audio and video files).  But good old 7-bit
email using the 128 ASCII characters could not do this.  There were several
efforts to extend this but the MIME spec (RFC 2045-2049) was the spec that
finally worked and was universally adopted.

Basically, the MIME standard allows for an email message to be broken into
specific named parts, with defined separator strings.  Further, non-plain-text
parts (e.g. arbitrary binary data) can be 'encoded' or converted into 7-bit
plain 128 ASCII characters for safe transmission by email, and then 'decoded'
(converted back to original format) at the receiving end.  The specs for
'parts' separator strings and encoding/decoding methods are part of the MIME
standard.

The spec provides rules for the separation of message parts and the encoding
methods of each part so the receiving mail program can follow these
'instructions' so it can correctly decode and reassemble the message into its
original format.  HTML emails usually are a really a multipart/alternative
message consisting of a plain-text part and an HTML part.  Also there may be
multipart/related attachments consisting of graphics, images, audio or video
files, etc.

When received as an individual or single message almost every email program
can correctly decode and display the message and its related parts
(attachments, such as images of favorite dog).  But, although there IS also a
standard for formatting Digest messages (an accumulation of several single
MIME messages with all of their component parts), most designers/programmers
of email client programs got lazy and ignored this standard for Digest
messages.  

Thus the current situation where some mail clients work better with one kind
of Digest setting and others work better with another.  It is NOT the fault of
LISTSERV.  It IS the fault of mail client programmers who failed to follow
defined standards and thus doomed their users of that mail client program to
'Digest Purgatory' because their particular program failed to follow the
standards and thus failed to be able to correctly display a MIME message with
its component parts and attachments, if any.

So, since nearly all email clients (including webmail clients like gmail,
hotmail, yahoo, etc.) now allow filtering mail to user defined folders (tip to
Valdis), why even bother with Digests nowadays?  Correct handling of digests
remains problematic due to lazyness of some programmers, but filtering/folder
assignment is a major workaround, that allows recipients to essentially build
their own 'digest' in a folder of their choice.  

LISTSERV has many features.  Some were meant to address ancient issues with
certain mail clients (anyone remember CC:Mail?).  They may no longer have a
useful place in today's email environment.  Even less so in the WWW-centric
blog/facebook/twitter interface of the future.  

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