Go in to your ebay account. Click on the 'my ebay' tab and then click 'messages'.
If it is genuine (it isn't) it will be there but your mind will be put at rest.
You should do that for all emails you get concerning bank accounts, ebay, paypal - everything. Don't click on links in the emails, open the website in your browser and log in there.
If you have never created an account - perhaps you get an email from the Inland Revenue - google the phone number of the company/organisation and speak to them.