On July 15, 2014, Google enacted changes to security for accessing its web-based applications. For many, this meant applications like email clients stopped working unless changes were made to Google account settings. Google labeled the change as restricting use of "less secure apps" which really meant it was turning off access to those applications using Basic Authentication as a connection method. It's a good thing and should make communication more secure.
Within your online account settings you can still opt to use the old Basic Authentication method, but as one reader and commenter put it: "Why reduce security when you can simply create specific application passwords for any client that accesses your Google account?"
And, that's a good point. Fortunately, Google offers the ability to set specific passwords for specific Google apps running on specific devices.
To setup passwords, login to your Google profile and go here: https://security.google.com/settings/security/apppasswords
For this option (and page) to be available, you must setup 2-Step Verification first. You should also note that once you setup 2-Step Verification, you can no longer opt to use Basic Authentication.