Yup, it's for real.
You have less than 100 listings, so probably relatively easy to check and see what's needed.
First make sure each item is actually in the right category - recently ebay took it upon themselves to move things around into different categories, so if any of your listings were moved, they would have lost their item specifics and have become "undefined", so nobody will find them in search criteria.
Secondly, if everything is still in its right category, then you would need to make sure the major items specifics are filled in.
There is a way to do this in bulk editor, but personally for 100 listings I would just rather go into each one, and see what (if any) recommendations come up as you go through the listing.
There may just be 1 listing in all of your items that needs attention.
I got the same email today and since I had already gone through the majority of my listings recently checking each one individually, there were only about 10 remaining that were problematic.
I didn't want to get sucked in to Optiseller, so I took the time to go through everything and double check it before the deadline. Yes, it was time consuming, but it also gave me a chance to eyeball each listing and make sure there were no errors either in the specifics or in the description itself.
Worst case scenario - if you don't update anything now, those listings will be removed from sale at the deadline, but you can relist them and update them at that time.
