We recently needed to create SPF records for one of our customers’ several email domains. Sender Policy Framework is implemented as a DNS TXT record and it’s designed to provide a mechanism to allow an email server to verify the valid IP addresses for a given email domain. The syntax can be a little tricky so I found several good sites to help generate the SPF. One of the best was Microsoft’s, which retrieves the actual IP addresses from DNS to build the TXT record. After you answer a few questions about email flow it creates the record which you can copy/paste into your DNS configuration.
 
https://www.microsoft.com/mscorp/safety/content/technologies/senderid/wizard/