[Bug 849416]

[Markus Kuhn]

Dear newcomers to this issue. As explained above in [comment
122](https://bugzilla.mozilla.org/show_bug.cgi?id=505024#c122), this
issue is really a bug (violation of the MIME standard) **in the calendar
function of Microsoft Exchange** that sends these messages. Regarding
Thunderbird, this issue is a **feature request for a workaround for a
violation of the MIME standard by a Microsoft product**.

For history buffs: The underlying issue is that Microsoft Exchange was
originally designed to be an in-house X.400 mail server that added an
Internet (RFC822+MIME) email gateway only later as an after-thought.
X.400 only allows a flat list of attachments, but MIME allows (and
requires in this case) a hierarchical tree of a multipart/alternative
inside a multipart/mixed attachment. Microsoft still has not yet fully
resolved all the ancient early-1990s legacy of the in-house X.400 mail
product that eventually became Microsoft Exchange, and probably as a
result their Exchange Calendar function keeps sending out malformed
MIME. (To better understand the complex ways of how Microsoft Exchange
internally maps RFC822+MIME messages onto their own X.400-style message
objects, see [[MS-OXCMAIL]: RFC 2822 and MIME to Email Object Conversion
Algorithm](https://docs.microsoft.com/en-
us/openspecs/exchange_server_protocols/ms-oxcmail/b60d48db-183f-
4bf5-a908-f584e62cb2d4). Warning, this is not for the faint hearted.
Don't use Microsoft Exchange if what you really want is proper
RFC822+MIME email. It never was. Spread the word.)

Repeat: this is a feature request for a workaround of a long-standing
Microsoft Exchange bug. This is not a Thunderbird bug.

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https://bugs.launchpad.net/bugs/849416

Title:
  text/calendar attachments are not shown at all

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