INBOX: invalid remote specification

Hello, I am new to mailhandler. I am trying to setup to retrieve from a gmail account.

But I get the following error:

Can't open mailbox {pop.gmail.com:995/pop3ssl/novalidate-cert}INBOX: invalid remote specification

All the documentation I've read say INBOX is the correct folder to specify.

Could you please let me know what "INBOX: invalid remote specification" means?

More info: I've had numerous issues just to get this stage. Before gmail would prevent sign-in because said unknown devic (my server) was not secure enough. I told it to allow less secure device here: https://www.google.com/settings/security/lesssecureapps