The first task in finalizing your Exchange 2016 hybrid deployment is to configure the Sender Policy Framework (SPF) record ...

The first task in finalizing your Exchange 2016 hybrid deployment is to configure the Sender Policy Framework (SPF) record in your DNS settings. The SPF record ensures that other email systems trust messages sent from your domain and from %BRAND_EXCHANGE_ONLINE_SHORT% Online Protection (EOP), the email filtering service used by %BRAND_OFFICE_365_SHORT%.