That is exactly how a Mendix-form responds to when (one of) the validation-rule is not yet returning true. You will need to first fill the textbox with a string-value that is an email, and only then you go to a next step like calling a nanoflow.
Validation in pages can be valuable, though my personal preference is to only use client side validations when direct user interaction is needed. When handling data, which will be send to the database, always validate at domain model level or in you commit logic.
Thus, skipping the validation on you email input box, remove the widget validation and if needed, execute the validation in your nano/microflow