Complex sentence: Furthermore, it paves the way for effectively exploiting policies like SPF that rely upon end-user SMTP authentication in order to block "email address abuse", but it prevents users of their own domain to publish a proper SPF policy.
Split into simpler sentences: Furthermore, it paves the way for effectively exploiting policies like SPF, which rely upon end-user SMTP authentication in order to block "email address abuse". But it also prevents users of their own domain to publish a proper SPF policy.