Tristan Miller Reporter
	Description • 7 years ago

When declining an event, some calendar clients will send a multi-part MIME e-mail.  One of these parts will be a text/html part containing a human-readable message, and the other part will be a text/calendar part containing the iCalendar entry updated with attendee info.

The problem is that Lightning displays only a suitably formatted version of the text/calendar part, not the text/html part.  This means that if someone tries to send me a message explaining why they are declining my invitation, there is no way for me to see it.  Changing the View->Message Body As settings does not work around the problem.

Attached are two screenshots of the same message viewed in Thunderbird 52.3.0, one with Lightning 5.4.3 enabled and one with Lightning disabled.  The HTML message is shown only when Lightning is disabled.  Also attached is the original message (with personal names redacted).

	Jorg K (CEST = GMT+2)
	Comment 4 • 7 years ago

Let's confirm this here since it has a reproducible test case.

	Jorg K (CEST = GMT+2)
	Comment 6 • 7 years ago

When opening the attached sample e-mail I see various errors saying that this time zone
  TZID:Amsterdam, Berlin, Bern, Rome, Stockholm, Vienna
isn't valid. Changing this to Europa/Amsterdam I run into further problems since the message is a reply declining an invitation and the original event is not in my calendar since I didn't send the invitation in the first place.

I thought this might be related to bug 1360155, but it's not.

MakeMyDay, since you did some duping here (which I undid), have you looked at this case?

	[:MakeMyDay]
	Comment 7 • 7 years ago

As I stands, we're doing the right thing already here. Since this is a multipart/alternative type message, displaying only the calendar part in this case is correct.

The sending party should have either included the message text in a comment property in the text/calendar part (which is something the Exchange Server in general is capable to do; comments if any are displayed in the invitation preview) or have sent the message as multipart/mixed, so it's basically a configuration issue of the sender (client or server).

Unfortunately, that doesn't really help a TB/Lightning user receiving such an invitation. The only option I see here would be to work around by relaxing the behaviour of the mime parser to treat even a multipart/alternative as multipart/mixed in case a text/calendar section is involved. But I'm not sure whether this is something we really should do.

	Tristan Miller Reporter
	Comment 8 • 7 years ago

(In reply to [:MakeMyDay] from comment #7)
> As I stands, we're doing the right thing already here. Since this is a
> multipart/alternative type message, displaying only the calendar part in
> this case is correct.

I agree.  However, it isn't *incorrect* to offer the user the choice of which part to display.  Quoth RFC 2046:

> It may be the case that some user agents, if they can recognize more
> than one of the formats, will prefer to offer the user the choice of
> which format to view.  This makes sense, for example, if a message
> includes both a nicely- formatted image version and an easily-edited
> text version.  What is most critical, however, is that the user not
> automatically be shown multiple versions of the same data.  Either
> the user should be shown the last recognized version or should be
> given the choice.

Offering this choice, via the View->Message Body As menu, seems to be what Thunderbird itself does with multipart/alternative messages where one part is plain text and the other part is HTML.  Why not provide similar functionality with Lightning?  Display the last (text/calendar) part by default, but provide some mechanism that allows the user to see the other (text/html) part.