Queue not receiving emails

I have followed the very good directions in the following link to set up my gmail account as the main mailbox for my Dynamics 365 instance:

https://community.dynamics.com/enterprise/b/dynamics365apps/archive/2017/01/08/how-to-configure-dynamics-365-to-receive-emails-from-gmail-using-pop3

and got the mailbox and associated queue to be successfully set up. 

However,  I have sent multiple emails from multiple different email addresses to get email messages into the queue but they do not appear, not as cases or as activities. They do not appear at all. I cannot figure out what the issue is.

Thanks very much for any advice.