Hi,
I know this doesn't help your problem. But I've been setting up some email presets for PM and your query got me a little concerned, so I tested sending an original image (as above) to see if everything worked.
I sent a file 2.6MB file using Apple's Mail app (PM estimated it would be a 5.02MB) and the file received was exactly the same size as the original, 2.6MB (2,574,710 bytes). So the original file was indeed sent and received.
As I say, I appreciate this doesn't help your problem, but I just wanted to confirm that it should work. (PM 4.6.9 using MacOS 10.8.2)
All the very best.
Cheers,
Tony