Here's what you need to do to get SPF checks working in Spamassassin which is really helping reduce spam and helps legitimate mail get through.
1. yum install perl-Mail-SPF
2. Create new file located here etc/mail/spamassassin/custom.pre
Add the following line:
loadplugin Mail::SpamAssassin::Plugin::SPF
3. Adjust scores accordingly in /etc/mail/spamassassin/local.cf
score SPF_HELO_FAIL
score SPF_FAIL
score SPF_HELO_PASS
score SPF_PASS