First, Gmail settings should be made as following:
SMTP: smtp.gmail.com
Port: 465
SSL: Checked.
User and password should be checked, you should use yoru full gmail address as the user and its password.
Additionally, Gmail had recently changed several security options which may block the printer from connecting to their servers.
First open the following link and ensure you are logged on to the same account as you are setting for the printer.
https://myaccount.google.com/
Within the Sign-in & security section click on Signing in to Google and ensure that "2-Step Verification" is set as "Off".
Within the left pane click on Connected apps & sites and ensure that "Access for less secure apps" is set as "ON", otherwise the verification will fail.
Within the left pane click on Device activity & notifications, witin the 'Recent security events' section click the Review events link and ensure there are no blocked connection attempt (it will be highlighted in red) , if there is any alert follow the steps on screen to ensure there is no block for that device.
