Summary: CONVERSIONS THAT LOSE INFORMATION ARE A NO-NO FOR MTAS!
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.
Suppose that in a particular case, any loss of information is
absolutely intolerable. How do I know that an image I'm receiving
hasn't secretly been converted to JPEG and back to GIF by conspiring
MTAs? Is there a way for the sender to specify that this is not an
acceptable step (e.g. to say that he'd much rather fragment the data
himself if the MTA won't do that)?
BTW, I think that the issue of convenience of GIF vs. JPEG for users
is a red herring -- soon enough, JPEG will be as widely supported as
GIF (it sells itself quite well through its lesser disk space
requirements). E.g., there is already a version of "xv" that
--Guido van Rossum, CWI, Amsterdam <guido(_at_)cwi(_dot_)nl>
"Exploding is a perfectly normal medical phenomenon."