Corrupted email images
I once was able to send and receive picture email of any quality, including TIFFs. Recently, the largest pictures I can send and receive are medium JPEG. I’m running an iMac on OS X 10.6.8 and a 13-inch MacBook on OS X 10.6.8. (The MacBook pictures are less corrupted.) I’ve checked every setting on Mail, Safari and Internet Utility, to no avail… A J Brookes This is a subtle and long-standing bug in the way that Mail handles 64-bit message encoding. I first saw it with Lion and it has persisted through Mountain Lion and Mavericks. I haven’t had positive confirmation that it’s still there in Yosemite, but I haven’t seen a change log that reports it fixed yet, either. It’s caused when email attachments are converted using the base64 encoding system, so that they can be accepted by email servers. Anecdotally, it seems that dragging an image into an email that already contains some text can occasionally trigger the problem, but attaching it using File > Attach Files never will.
What’s more certain is that attaching images through a webmail interface (such as gmail.com) never causes the problem. You may be able to fix existing corrupted images by entering defaults write com. apple.mail DisableInlineAttachment Viewing -bool yes in Terminal and then clicking Mailbox > Rebuild in Mail, to force them to download from the server again.