1. I am using IE9 on Win7-64; but it doesn't make any difference on my IE11 laptop.
2. Sent myself a jpg:
a. no thumbnail,
b. clicking on blank thumbnail provided me with the "Sorry, we are unable to display this attachment"
c. "Save to my Computer" option now seems to be working without corrupting the file.
3. IE version does not seem to be the problem. The very same thing happens on my HP laptop with with 8.1 IE 11
4. Tried the same thing on my wife's computer which is registered to a different email account, and she is not experiencing any the problems I have experienced, using my account.
5. So . . . the glitch would seem to be isolated to MY account.
6. After sending a failed test jpg to my account, 20 minutes later I repeated the procedure, sending the same jpg to both of our accounts, and both accounts now display normal thumbnails in the traditional fashion, with full rendition upon clicking on the thumbnail.
Let's hope that the problem is being actively addressed; and the current problems are merely a momentary glitch.