A Sender Policy Framework (SPF) record indicates mail servers that are authorized to send mail for a domain. Email recipient servers perform a check with DNS to see if the mail came from an authorized server. If not, then the email is most likely SPAM. SPF DNS records lets the recipient server perform this verification.
A DomainKeys Identified Mail (DKIM) record adds a digital signature to emails your organization sends. Email recipient servers perform a check with DNS for the to see if the DomainKey matches the sender. If so, then the email is considered unmodified and from a legitimate sender. DKIM DNS record lets the recipient server perform this verification.
Configure Google Apps SPF
If you use Google Apps for email, you’ll need access to your DNS provider to add an SPF record. In most cases, you simply login and create a new TXT record with the value of:
Send an email from your Gmail account to check–firstname.lastname@example.org after you’ve completed the Google Apps SPF and DKIM setup. You’ll receive an email response in a few minutes. If everything is properly configured, you’ll receive a “PASS” for both the Google Apps SPF and DKIM settings. This means your email is now securely being delivered and can be verified as such.