I have recently started getting broken images in Mail.app. Often, when someone sent me relatively big pictures (over 1 MB in size), the image ended up being corrupted, with a smaller file size that one would expect. This results in a picture that’s visible up to a certain point, and then rest is usually filled with solid grey by the viewer. While this could happen because the attached image is indeed broken — that is, if the sender is attaching an image that’s already corrupted on his/her machine —, it’s unlikely that the file gets mangled during the transit. To begin with, the base64 encoding adds lots of CRC (1/3 of the file size, and this alone explains why it’s a very bad idea to send big files through e-mail). In addition to that, no MTA will accept a malformed message: MIME parts must be completed with an extra boundary…