Restrict Google Apps domains with Google account using O365 email

Hi Rodrigo Silveira1,

Thank you for reaching out to Sophos Community.

'Restrict login domains for Google Apps' option allows users to sign in to Google services only with the domains specified. It is mostly used for GSuite accounts(Corporate Google account).

Could you please us more about your query?

Hello on this customer, their email is hosted on Office 365, but with that same domain they are registered on GSuite to use Gdrive and other apps, but I think Sophos didn't recognize it as a Google domain because in fact it is not and therefore the XG doesn't allow the user to log on to the Google services with that email.

Hello Rodrigo Silveira1, 

Can you confirm if the domain "example1.com" has been populated into the UI field requesting a "comma-separated list of allowed domains for Google Apps"? 

Please refer to the Google Documentation here:
https://support.google.com/a/answer/1668854?hl=en#zippy=%2Cstep-choose-a-web-proxy-server%2Cstep-configure-the-network-to-block-certain-accounts

The XG is taking the contents of the "list of allowed domains" field configured and putting it into the Header that Google would like.  All enforcement is done by Google.