If you are a Google Workspace customer and you have on-premise servers that do not support SPF authentication or DKIM signing you can configure them to relay the emails via Google Workspace. This relay would allow your emails to properly authenticate and pass DMARC as Google Workspace will do the SPF authentication 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 Google Workspace with DKIM please click on the button below.