Can not send or receive any new mail by MIAB 0.47

I can not send or receive any new mail by Mail-in-a-Box v0.47.
How can solve this problem?

I get the score 10 from https://www.mail-tester.com/.

How? If you can’t send or receive any email…

What does the status check page say when you run it in the admin area? Anything out of the ordinary?