SPF is a way for the receiver to validate if a specific sender is authorized to send mail on behalf of a specific domain.  This is done via a DNS TXT record lookup.

To create a Google SPF record for a domain:

  1. Log in to the administrative console for your domain (where your DNS is hosted).
  2. Locate the page from which you can update the DNS records.
    You may need to enable advanced settings.
  3. If you already have aTXT record set up for SPF, then modify the record to be the following, otherwise create a TXT record containing this text: v=spf1 include:_spf.google.com ~all
Note:  There can only be one SPF record per domain.  If you require more values added to the TXT record (in cases where you have other authorized email servers, or services, you can also add those to the SPF record.  

Example of a multiple value SPF record:
v=spf1 ip4: include:_spf.google.com ~all

In order to validate your SPF record, you can use the following URL, which will check your current settings.