Properly Formatted Return URL for PayPal Express Checkout

I use PayPal Express checkout. Inside my PayPal account under 'website payment preferences' I had auto return switched on but to my horror the retrun URL pointed to my old (host servers) website (same domain name) no longer in use. Does this mean that for the last couple of years all my customers have been re-directed in cyber space (I have had no complaints)? How do I set-up a properly formatted Return URL? Or do I not need to do this because Express checkout automatically takes care of this (I should be so lucky). Urgent response required please!

PayPal normally returns customers back to the site where the transaction was initiated.

Example: You may have 3 different ZC installations, all different shops and URL's but only one PP account. PayPal returns the customer back to the URL where the transaction comes from.

I have two shops in 2 different sub domains and each transaction is handled individually - back to the original store.

Thank for that! It makes sense, so I can forget about the website preferences page in my PayPal account.

You should still set it to a valid address, just in case you do transactions in PayPal that are not initiated by your store, such as sending money to a friend etc.
ref: http://www.zen-cart.com/wiki/index.php/PayPal

Thanks for all the help :D