HTAutocompleteTextField is a subclass of UITextField that automatically displays text suggestions in real-time. This is perfect for automatically suggesting the domain as a user types an email address.
HTAutocompleteManager (included in the example project) provides email address autocompletion out of the box. It comes with a list of the top email domains based on the HotelTonight customer database. You may want to tailor this list of email domains to match your own customers, or you may want to write autocomplete logic for a different type of text field (in the demo, names of colors are autocompleted).