If you don’t currently have an SPF record for your domain, add the following TXT record to your DNS, using the normal method
“v=spf1 include:gms-cloud.com”
Which should end up with a record that looks something like this:
domain.dom IN TXT “v=spf1 include:gms-cloud.com ~all”
If gms-cloud isn’t the only place that will be sending mail for your domain, you’ll need to add the include:gms-cloud to your existing record, so you end up with something like this:
domain.dom in TXT “v=spf1 include:spf1.domain.com include:spf2.domain2.com include:gms-cloud.com”