Some email programs have a limit on the maximum size for a single transmission. You could hit this limit on the sending OR receiving end, and in some cases, the message and attachments are silently discarded. I've seen this limit as low as 5 MB. I don't know if MS Digital Images sends the images directly, or if it uses your default email client. But it's also possible that MS Digital Images is simply choking or timing out due to the huge attachment you're generating.

There are two possible solutions to your problem. Remember the old joke where the guy goes to the doctor? He says "It hurts when I do this." So the doctor says "Don't do that." JPEG image files can be quite large, depending on the resolution of your digital camera. So your chances of getting the emails successfully sent AND received are much improved by sending smaller batches. You can also reduce the resolution and size of the images with your photo editing software. If your application doesn't demand super high resolution, you can probably reduce the file sizes by a factor of 5-10X. And that will allow you to send more images in a single batch.