$ git clone https://github.com/w3p/php-spf
$ cd php-spf
$ phpize
$ ./configure
$ make
$ sudo make install
$ echo "extension=spf.so" > /etc/php5/conf.d/spf.ini

void        Spf::__construct([int $type[, string $domain[, string $spf]]])
SpfResponse Spf::query(string $ip, string $helo, string $sender[, string $recipient])

string  SpfResponse::getResult();
string  SpfResponse::getHeaderComment();
string  SpfResponse::getReceivedSpf();
string  SpfResponse::getReceivedSpfValue();
string  SpfResponse::getExplanation();
string  SpfResponse::getSmtpComment();
boolean SpfResponse::hasErrors();
boolean SpfResponse::hasWarnings();
array   SpfResponse::getErrors();
array   SpfResponse::getWarnings();