Re: MIME part header (was: SMTP headers)

On Thu September 14 2006 13:47, Frank Ellermann wrote:

> For a plain text US-ASCII part you generally need no header
> fields at all (for the default inline disposition).

There is no such thing as "default inline disposition".

A MIME-part has inline disposition if and only if it contains a
Content-Disposition MIME-part header field specifying inline disposition.

In the absence of a Content-Disposition field, quoting RFC 2183:
"   Content-Disposition is an optional header field. In its absence, the
   MUA may use whatever presentation method it deems suitable.
"

N.B. the default behavior is a characteristic of the specific MUA in use, not
of the MIME-part.

Also note that specified but unrecognized dispositions are treated as
equivalent to "attachment", again quoting RFC 2183:
"  Unrecognized disposition
   types should be treated as `attachment'. The choice of `attachment'
   for unrecognized types is made because a sender who goes to the
   trouble of producing a Content-Disposition header with a new
   disposition type is more likely aiming for something more elaborate
   than inline presentation.
"

On a related note, a MIME-part with no corresponding Content-Disposition
header field does not have semantics of "attachment", regardless of what
'KANA Response' and some other MUAs may label them.  More pointedly, a
MIME-part explicitly labeled as "inline" disposition most certainly does not
have semantics of "attachment", such broken MUAs' claims to the contrary
notwithstanding.