Servicedesk Install - Inbound mail settings

Hello,

I'm attempting to install Servicedesk and configure the inbound mail settings (POP) and running into issues with the test. 

When I select not SSL I receive the following error " The username was not accepted on the server"

When I select SSL I receive the following error " Could not connect because of an authentication error:  System.Security.Authentication.AuthenticationException:  The remote certificate is invalid according to the validation procedure"