Nope. Sorry, but that does not seem to work. I get a notification saying' mail cannot open attachment'.
Hmmm...I don't know what to tell you then. I receive .jpg files from all sorts of folks (using Windows, Mac, Linux) and haven't had any problems saving and opening them on my iPad. In fact, these are all of the file types that the iPad supports...
Viewable document types: .jpg, .tiff, .gif (images); .doc and .docx (Microsoft Word); .htm and .html (web pages); .key (Keynote); .numbers (Numbers); .pages (Pages); .pdf (Preview and Adobe Acrobat); .ppt and .pptx (Microsoft PowerPoint); .txt (text); .rtf (rich text format); .vcf (contact information); .xls and .xlsx (Microsoft Excel)
So does this happen with every .jpg file you receive from everyone or only particular accounts? Are these original emails or forwarded? Can you send yourself a .jpg file and open it?
Without seeing the actual/original file I suspect there's something up either with the file itself or the mail sever from which it's being sent...having some effect on the attachment, but it's really hard to say.
About the only thing you can try on your end would be to restart or reset your iPad just to be sure it's functioning normally. Hold down the power switch (outside edge) by itself until the red slider appears. Turn it off by sliding the switch and then once again hold down the power switch until the Apple logo appears.
Resetting the iPad should be reserved for a non-responsive unit as it addresses other activity but if restarting doesn't do it, resetting it might. Hold down the power and home buttons until the slider appears and shut it down. Hold down the power switch again until the Apple logo appears. Fully booting up from a reset will take a little longer than a restart.
More here:
iPhone, iPad, iPod touch: Turning off and on (restarting) and resetting
If that doesn't work then I'm stumped. Again, the only thing I can think of is that the files you're being sent have something unusual about them. It might be worth discussing them with the sender.
Perhaps others will have some suggestions.
Best of luck and let us know how it goes!