Creating (or updating) your SPF record using the SPF Wizard at pobox.com:
Visit https://spf.pobox.com/wizard.html. Below is a screenshot of what you’ll see. Enter your domain in the domain field and click the begin button. Any domain settings already in place will appear. Then follow the guide below to generate your SPF record and add us to it. Be sure to consult your mail administrator for items related to your own mail servers.