I have only ever posted .jpg and my recent success was also.jpg.
There is not difference between .jpeg and .jpg. This is what Google has to say:
"There is no practical difference between JPEG and JPG files; they both refer to the same image file format created by the Joint Photographic Experts Group. The shorter, three-letter "JPG" extension originated from a legacy limitation in older versions of Microsoft Windows, which only allowed three-character file extensions. Modern operating systems no longer have this limitation, so most applications can open and interpret both file extensions interchangeably, making them identical in function. "