tcpserver Global Vars:
 SPF_ACTION   Type of action to take based on SPF result
 SPF_TARPIT   Enable/Disable tarpitting
 SPF_TARPIT_TIME   How long to tarpit for
 SPF_EXPLAIN_STATE   Enable/Disable 'SPF Explanations'
 SPF_EXPLANATION   Define the Explanation to message provide
 SPF_TRUSTED_STATE   Enable/Disable 'Trusted Forwarder' mode
 SPF_TRUSTED_FORWARDER   Define the Trusted Forwarder SPF Query to execute
 SPF_GUESS_STATE   Enable/Disable 'Best Guess' mode
 SPF_BEST_GUESS   Define the Best Guess SPF Query to execute
 SPF_HEADER_STATE   Enable/Disable 'Received-SPF:' header tagging
 SPF_DEBUG_STATE   Enable/Disable libSPF debug logging (/var/log/spf.log)
By setting these in your environment with appropriate values you can nicely alter the behaviour of libSPF for an individual person or groups of people on your network. A great example is by placing SPF_ACTION inside of tcp.smtp and setting it to a 0 for 127.0.0.1.
127.:allow,RELAYCLIENT="",RBLSMTPD="",SPF_ACTION="0"
This way 127.0.0.1 never has SPF checks performed on them. I'm sure you get the idea.