Setting up SPF involves adding a TXT record to your domain's DNS settings. Here's a step-by-step guide:
Log in to your domain hosting provider. Navigate to the DNS management section. Add a new TXT record with the name 'v=spf1 include:_spf.yourprovider.com ~all'. Replace 'yourprovider' with your ESP's domain. Save the changes and allow some time for the DNS to propagate.