Gmail has apparently started blocking PPop Peeper,
Stating the following
Less secure app blocked
Google blocked the app that you were trying to use because it doesn't meet our security standards.
Some apps and devices use less secure sign-in technology, which makes your account more vulnerable. You can turn off access for these apps, which we recommend, or turn on access if you want to use them despite the risks.
You just need to enable OAuth2 -- edit the account in POP Peeper and then press the "OAuth2" button to the right of "Login name" and follow the instructions.
