How do I get the email of the one submitting contact form in the "reply to"? Drupal 8 site. I'm using the core Contact module for basic "Contact Us" form.

How can I get the email of the person submitting the form to be in the From field? And a follow-up: How do I get the email of an authenticated user to show in the body along with the username?

Site and users:

The site is an association website. There are about 100 user accounts.

Domain and email:

The site domain is not the same as the email domain in account settings: the site is theirsite.org and the email is theiremail@gmail.com

From &amp; To in email

When the email came in from authenticated user or anonymous user, the From and the To are both showing theiremail@gmail.com - the site email.

What shows in body of email:

The email from the authenticated user does not show in the body of email; only the user name and the link to their user account /user/[user-number]

When I submit a form as an anonymous user the email does show in the body.

P.S. I do not want to use the Webform module.
If the person submitting the form is an anonymous visitor the form will be empty and the visitor will have to fill in every field. 

If the visitor is logged in (authenticated user) the name and email address are already pre-filled from their user profile. 

Are you sure you're not testing this while being logged in as an admin account that has the same email address as the site? Then it's expected to see that email there. 

Try to login as a different user, and also test as anonymous to see that the email is now from that different user/empty respectively for those two cases. 

If you're constantly seeing the site email as From in all three cases then it's a bug and you should try to see where it's coming from. I haven't seen any problems with the Contact module, it's showing the correct "From" value every time.