This ascertains if the submitted data is a valid email address.
Error message - The message to display next to the element if the Validation fails. This text should explain why the Validation failed and what steps the user should take to remedy the error.
Condition - A PHP expression which if returns false, means that the Validation is not run.
Allow empty - If set to yes the Validation will allow the user not to enter an email address, if set to no then an empty value will cause the Validation to fail