I am working on a site where a user will input an email address, it will then need to be checked whether or not that email exists in a database, and only if it exists can the user continue. What I would like ideally is an input field where the user writes the email, then below that a line which shows either green for 'email found' or red 'email not found, try again'. I also want the user to be unable to continue if the email field is filled in, but giving the 'not found' message.

I have been searching for hours for a tutorial on this, but so far could not find any.

Any help would be greatly appreciated!