[Mailman-Users] Could Mailman cope with extra Mime sections intended for Apple Watches?

Mark Sapiro mark at msapiro.net
Mon May 18 01:59:18 CEST 2015

On 05/17/2015 04:04 PM, Peter Shute wrote:
> This isn't something that's happening right now, and I doubt it will,
> but you never know. Apple is playing with mail formats intended to
> display as a message summary on an Apple Watch, but show the full
> message on a larger device. Apparently it's a legal format, but lots
> of mail clients are getting it wrong, and I'm wondering what Mailman
> would do with a message like that.

Process it in conformance with the MIME RFCs and the list's content

> It's being discussed here, and someone has posted a sample of the
> format: 
> https://discussions.apple.com/thread/7039218?start=15&tstart=0

I looked at that, and it appears the structure of the message is as follows

            plain text version
            html 'summary'
            html version

This is arguably non-conformant. multipart/alternative parts are
supposed to contain sub-parts which are alternative representations of
the message arranged in increasing order of complexity, and MUAs are
supposed to render the most complex (supposedly closest to the original)
that they understand. The summary part is not a more faithful
representation of the complete message than even the text/plain part, so
it doesn't belong there.

What mailman will do depends on content filtering as follows:

filter_content = No or filter_content = Yes and both text/html and
text/plain accepted (in pass_mime_types) and both collapse_alternatives
and convert_html_to_plaintext = No

In these cases the message will be delivered as received, except if
filter_content is Yes, the multipart/mixed outer part with only one
multipart/alternative sub-part may be collapsed to just the multipart
alternative part.

As above but collapse_alternatives = Yes

In this case all the alternatives other that the first (text/plain) will
be removed. This is essentially the same whether or not there is a
summary part.

if collapse_alternatives = No and convert_html_to_plaintext = Yes

All three parts will remain and all will be converted to text/plain and
it will be up to the MUA to pick one which should be the text/plain
conversion of the full message HTML part.

There are other possibilities such as text/html not accepted in which
case only the original text/plain part will remain.

In short, Mailman will do the right thing, but Apple watch users
probably won't like the result in some cases.

Apple is notorious for playing fast and loose with email. I don't know
if it's still the case, but at one point, Apple mail would let you drag
and drop pictures into a plain text email so it would look to Apple mail
users as

some text
more text

with a MIME structure like


and Apple mail would render what the sender saw and every other MUA
would see a text/plain message with 4 attachments.

Mark Sapiro <mark at msapiro.net>        The highway is for gamblers,
San Francisco Bay Area, California    better use your sense - B. Dylan

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