SMTP Authentication Guide for Gmail for Android
As has been advised in our communication, if you use a third party program or application to access your email you will need to ensure that the settings for the Outgoing Mail Server “SMTP Authentication“ is now ticked and your email address and password is entered into the authentication details.
You will be required to make this change to the settings in order for you to be able to authenticate with the server and be able to send and receive email. Instructions on how to check this can be found below:
For instructions on how to enable SMTP Authentication in Gmail for Android application, click here
Currently enabling “SMTP Authentication” is not a requirement for your email to work. However once the migration has been completed it will be therefore it is important that you check this setting.