Content-Disposition: =?utf-8?Q?inline?=
...
It seems, however, we should simply follow RFC 2183 and treat it as an
"unknown" disposition (which means "default as attachment").
I disagree. :-)
I understand where you're coming from given a strict reading of the
ABNF, but ... it's not clear to me what's supposed to happen if you fail
to parse that header. I know some people think that nmh should execute
"rm -rf /" if it ever sees an invalid message (not really, but it sure
seems like it sometimes), but we're alone in MUAs in our refusal to process
messages when we hit something invalid. I would argue that the "unknown"
disposition covers the "cannot parse disposition" case.
--Ken