if you are a GSuite customer and you have on-premise servers that do not support SPF and/or DKIM signing you can configure them to relay the emails via GSuite. This relay would allow your emails to properly authenticate and pass DMARC as GSuite will do the SPF and DKIM signing on behalf of your domain. 

For more information on what the SMTP service is and how to configure it please click on the button below. 

For information on how to configure your domain in GSuite with DKIM please click on the button below.