To add an SPF TXT record by using the Cloud Control Panel, follow these steps:
Log in to the Cloud Control Panel.
In the top navigation bar, select Networking > Cloud DNS.
Click the action gear next to the name of the domain that you want to modify, and select Add DNS Record.

Select TXT Record for the record type.
Enter the rule in the Text area. For example, enter v=spf1 mx -all to indicate that all email is sent from this server and no other mail servers are authorized.
Specify the Time To Live (TTL).
Click Add Record.