Excerpts from internet.ietf-822: 15-Apr-92 Re: Implications of MIME fo..
Guido van Rossum(_at_)cwi(_dot_)nl (1368)
Summary: CONVERSIONS THAT LOSE INFORMATION ARE A NO-NO FOR MTAS!
Guido is right on the general principles here, but I think the specifics
are more complicated. For example, JPEG encodings can tradeoff picture
quality vs. bandwidth in a way that makes it at least plausible to think
about reducing the size of gif images without enough loss of picture
quality to bother most users.
I would really rather not have any MTA making this decision, especially
since we are talking about intangibles such as "enough..quality to bother
most". This is a UA level decision, IMHO.
Moreover, we already know that it is within the bounds of reasonableness
for MTAs to reject mail based on size. Now, if someone sends me a GIF
image, and the MTA says its too big, I'd much rather get it as a
lower-quality JPEG image than not get it at all, at least in most cases.
So I think the bottom line is that this is not nearly as cut and dried
as you imply. While I'd rather never lose information, I'd often rather
lose a little information than all of it!
You and I may agree that a JPEG (with appropriate parameters) version of
the original is appropriate. We can negotiate and resend, etc. I don't
see this sort of interaction with the MTA. If specific agreements between
UA's and MTA's exist, I suppose that's alright. But I think the authority
must not reside at the MTA level.
The solution I'd prefer is to use message/partial and keep all the
information intact. Although this has a drawback if the receiving side
isn't MIME aware, this still seems to me to be a more reasonable attempt
at delivery than a possibly unauthorized conversion.