Try Ksar as if it were your site.

The 3 tries

1. 1

   A normal address

   The account is created and the promo offer granted.

   Try it
2. 2

   A disposable address

   The signup is blocked.

   Try it
3. 3

   The same person coming back

   With a +alias or dots: account created, but promo offer denied.

   Try it

Private sandbox, erased after 24 hours or as soon as you click "Start over". No address is stored in clear text.