I notice the TO (A) field there is an email address, but it is in red font and does not look like it has formed a 'pill' shape/ darker background rectangle with text on top.

How did you start to create the email? Did you click on a 'Reply' button or is this a clean new Write email?

What happens if you put mouse cursor at the end of the @nsg.it and then press Enter ?

Red font used to mean email address is not in address book. Are you able to access the Address Book ? Can you see address books and contacts? Is that contact/email address in one of your address books ?