You can't, SHA-2 is a requirement for Gmail and Office365 as of January, this model doesn't support it at all, so it is impossible to work with Gmail fully, or directly.
You can send from a gmail account to another gmail hosted account via the APSMX server, but not to any address that is not hoisted by gmail ,Godaddy, yahoo, MSN etc etc. But you would be better off using a relay like SMTP2Go.
Xerox/FujiXerox development has no intention of updating the machine to support SHA-2