This error is due to invalid DNS records included in the SPF.

You may refer to the following video for a full explanation -

https://app.screencast.com/FFcFL08Etj5bg 

<iframe scrolling='no' frameborder='0' style='width: 2100px; height: 1080px; border:0;' src='https://app.screencast.com/FFcFL08Etj5bg/e' allowfullscreen></iframe>