Multiple SPF records are not recommended and will cause authorization problems. Instead, update the existing record.

You can update your domain’s existing SPF record to authorize a new or additional mail server. For example, if you set up an outbound email gateway, your SPF record will include the G Suite server address and the outbound gateway SMTP server address.

To add a mail server to an existing SPF record, enter the server's IP address before the ~all argument using the format ip4:address or ip6:address. For example:

v=spf1 ip4: ~all

To add a mail server’s domain, use additional include statements for each domain. For example:

v=spf1 ~all