Sending message without recipients

I have realized it is possible to send an e-mail without recipients: no To, CC or BCC.

Email is sent, and then returned as there are no recipients.

Interface should validate whether the To, CC or BCC fields are filled and act accordingly.

Regards,
Carlos Dourado

Error message from Mailer-Daemon@runbox.com

“A message that you sent contained no recipient addresses, and therefore no delivery could be attempted.”