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.
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!