SPF stands for Sender Policy Framework, and it is the standard established in RFC 4408. Essentially, SPF validates emails sent to a mail server to determine if a message is spam. One of the biggest problems faced by ISPs trying to fight spam is the spoofing of IP addresses and domains. In such cases, blacklisting an IP address has little effect, since the spammer can use false ones. SPF is a system for validating emails before they are delivered.
SPF works by not allowing senders to forge FROM addresses. When a server establishes its mail server, it will broadcast that it only sends mail from certain systems. If a machine not on the list sends a message from the domain, the SPF-enabled server will reject it.
The benefit of SPF is that ISPs and hosting providers can set standards for mail delivery, denying message senders that do not provide valid SPF records. The unfortunate reality, however, is that the standard requires ISP adoption, and without it, SPF records are rather useless. If, for example, one ISP enforces the standard but another does not, spam can still be sent from one to the other.
It is not terribly difficult to setup SPF records on your dedicated server. OpenSPF.org even has a setup wizard on their website to make it easier for hosting providers and server administrators to include them in their DNS records. One setup, it does not require any further action on your part, and you will be contributing to create a more clutter-free Internet.