Client-side validation

One of the rules of application security is to never implement client-side validation but rely on server-side validation.
I came across an e-card greeting on the "Uniquely Singapore" website and decided to try it out. Hmmmm... the form doesn't allow me to submit an e-card with the recipient and sender emails being the same. Did they implement client-side validation? I decided to disable Javascript in Firefox. I reload the webpage and resubmit. Viola!!! Email sent and received.

This confirms that Javascript is used to validate submissions on the client's machine. The secure way would be to validate on the server so that the client cannot manipulate requests to successfully bypass validation.