Re: [Jmap] Attachments and composing more complex MIME structures

[Neil Jenkins <[e-mail]>]

On Tue, 8 Aug 2017, at 10:31 PM, Josef 'Jeff' Sipek wrote:
> Is there a MIME-aware client that breaks with what the iOS client
> generates?
I don't know; I haven't tested this exhaustively. I know we had bugs
with this multipart/mixed style at one point, since it was pretty
uncommon so I wouldn't be surprised if there were bugs or lack of
support elsewhere too.
More importantly, plain text is deeply problematic on mobile because of
hard wrapping. Format=flowed has zero traction[1], so you mostly end up
with hard wrapping that breaks in *really* awkward positions on many
mobile screens, as it normally presumes you can fit 80 chars in a
single line.
> In theory the multipart/mixed approach should be **more** compatible
> than HTML, since the client doesn't have to deal with HTML on top of
> dealing with MIME anyway.
Maybe, but I wouldn't be surprised if the MIME handling in some clients
extended only to "find the right part to show".
> As a mutt user that likes text/plain emails... it'd be great if these
> generated emails displayed nicely with non-HTML based MUAs. :)
There's no reason why the server can't generate a reasonable textBody
component as well (it will have to do this as well as htmlBody in this
case anyway). I believe you could build an excellent plain-text only
client on JMAP if you wanted, although realistically all modern email
clients have to deal with HTML.
> Is the goal to make only the simplest of clients easy to implement?
> Where does one draw the line between simple enough to use the nice
> jmap interface and too complex (IOW: just implement the whole RFC
> 5322/MIME/etc. stack and use the blob API)?
I believe you could implement the functionality of most modern GUI email
clients without resorting to MIME parsing. This is basically the goal:
most clients never need to deal with the raw message, but some with
support for less common features can do so if they want (like for
S/MIME). For example, I believe you could implement all the
functionality in the iOS/macOS Mail apps using the JMAP Message object,
although the implementation underneath might vary in some aspects like
the one we're discussing.  (Neil, do you agree?).
Neil.

Links:

  1. https://blog.fastmail.com/2016/12/17/format-flowed/