When you're entering an email address into a Contact Record, Rex performs a very basic validation of the address. If it's been entered incorrectly (a comma instead of a full-stop, for example), it'll immediately be underlined in red with the error message 'The email address 'firstname.lastname@example.org' is not a valid email address'.
You won't have the option to mark an incorrectly entered email address as valid. You'll first need to correct the email address:
- Click on the email address in the Contact Module
- Remove the error (comma, question mark, etc)
- Click out of the email address (anywhere else in Rex)
- Click Save Changes