Update Your Old Kindle Tonight
If you have an old Kindle sitting around that you haven’t used or updated in a while, dust it off and update it tonight. Otherwise, Amazon warns that it won’t be able to connect to the Kindle Store or sync with Amazon’s servers. All you need to do is fire up the Kindle and choose Sync and Check for Items in the main menu. If you don’t see this warning in time, it’s not the end of the world. After 21 March 2016, you can still update your Kindle via USB to enable it to connect once again with the Amazon mothership.
I may be wrong, but I don't recall seeing any email notification from Amazon regarding this matter. I receive a fair number of emails from them daily, so it's unlikely I missed it. Makes me wonder about the roll of Amazon’s customer service department.
Could have been caught by a spam filter along the way - it's really hard to depend on email for that sort of thing. Tonya did get email about it for our Kindles.