We had a customer call us, complaining that they could not download their Gmail electronic mail using Microsoft Outlook.
We verified that the correct POP & SMTP servers had been specified in the Outlook settings, as well as the security SSL ports. Despite this fact, they could not connect to Gmail.
We have discovered that since July 15th, 2014, Gmail has changed the way that 3rd party clients such as Microsoft Outlook are allowed to connect to Gmail.
To resolve this problem, enable Basic Authentication for your Gmail account. To do this, go to the following Google website, and then select Enable when you are prompted about whether to let less secure apps access your Gmail account: