The given verb recevoir is not listed in the hints as at 4th Sept 2020.
Why can't I use beaucoup de poste?
La poste is the mail service, not the actual mail you get in your mailbox.
"I don't receive a lot of mail". should be accepted.
Using Duo's Dark Mode there is just blackness before your 'is the mail service, not the ... '.
Thought you'd like to know.