The SPF is relatively young and was recently known as experimental, this technology is not yet very widespread. To be able to use it to eradicate spam, all domains in the world would have to set the appropriate (and properly defined) SPF records and all SMTP servers in the world would have to carry out appropriate inspections. You have to be careful at the correct set of rules for SPF record. If you mistakenly forget about some computer or a subnet it might be a problem with the delivery of regular e-mails. There are domains for which SPF rules can not be set – for example at free mail services such seznam.cz, of which e-mails are sent from anywhere.
As follows, for example, seems appropriate TXT record for domain ietf.org (shortened):
v=spf1 ip4:188.8.131.52/26 ip6:2001:1890:1112:1::0/64 -all
In the example we can see clearly defined subnets that are allowed to send e-mails to the address containing the domain ietf.org.