Thank you for your message.
Im afraid that this will not be possible as we are not using HTML 5 for CMS Desk/Site manager. There is probably some built-in check which checks these field.
For our form controls its best to use the validation we offer in code behind. You could setup the e-mail validation like:
bool IsValidEmail(string email)
var addr = new System.Net.Mail.MailAddress(email);
I hope this helps.