IT:AD:Google Apps:HowTo:Create an SPF Record for a Domain
Summary
If your domain is used to send out an amount of email beyond trivial, you'll want to create an SPF record for it so that your mail is not mistaken for SPAM.
As per Googles Documentation:
We recommend that you create a Sender Policy Framework (SPF) record for your domain. An SPF record is a type of Domain Name Service (DNS) record that identifies which mail servers are permitted to send email on behalf of your domain.
The purpose of an SPF record is to prevent spammers from sending messages with forged From addresses at your domain. Recipients can refer to the SPF record to determine whether a message purporting to be from your domain comes from an authorized mail server.
For example, suppose that your domain example.com uses Gmail. You create an SPF record that identifies the Google Apps mail servers as the authorized mail servers for your domain. When a recipient's mail server receives a message from user@example.com, it can check the SPF record for example.com to determine whether it is a valid message. If the message comes from a server other than the Google Apps mail servers listed in the SPF record, the recipient's mail server can reject it as spam.
If your domain does not have an SPF record, some recipient domains may reject messages from your users because they cannot validate that the messages come from an authorized mail server.
Proccess
See: https://support.google.com/a/answer/178723?hl=en
For these instructions:
To create an SPF record for a domain:
Log in to the administrative console for your domain. Locate the page from which you can update the DNS records. You may need to enable advanced settings. Create a TXT record containing this text: v=spf1 include:_spf.google.com ~all
Publishing an SPF record that uses -all instead of ~all may result in delivery problems. See Google IP address ranges for details about the addresses for the Google Apps mail servers. If your registrar also requires a host setting (such as @), see the TXT records for specific domain providers list for precise instructions. Save your changes. Keep in mind that changes to DNS records may take up to 48 hours to propagate throughout the Internet. If you have difficulty creating an SPF record, contact your domain provider for assistance.