Sun Java System Messaging Server 6.3 Administration Guide

15.2 Limitations

SPF is only one tool to use to fight spam, and will not address all issues. It is fairly easy for a spammer to create a domain and add an SPF TXT record that will make the domain seem legitimate. On the other hand, SPF is pretty effective for detecting forged email from established ISPs, although many TXT records will allow the SPF to not fail.