sendmail-8.12.10/11 HOWTO

unpack libspf
change into that directory
make
cp libspf.so.1.0.1 /usr/lib/libspf.so.1.0.1
cp spf.h /usr/include
cd /usr/lib
ln -s libspf.so.1.0.1 libspf.so.1
ln -s libspf.so.1 libspf.so

Perhaps you have to use /usr/local/include and /usr/local/lib instead
of /usr/include and /usr/lib

SENDMAIL:

unpack sendmail-8.12.10
change into that directory
patch -p0 < ../sendmail-8.12.11-libspf.0.xx.diff 

The output for the patch should look like:
-- BEGIN PASTE
patching file sendmail/readcf.c
patching file sendmail/Makefile.m4
patching file sendmail/sendmail.h
patching file sendmail/srvrsmtp.c
patching file cf/feature/spf.m4
patching file cf/m4/proto.m4
-- END PASTE

Then build sendmail as you normally would.

To enable SPF you have to add the feature spf. So in your
configuration-File sendmail.config.mc add the minimal
configuration-line

FEAUTRE(spf)dnl

If you want to config SPF you can add also the options to the
featur line:

FEATURE(spf, `SPFAction', `SPFHeaderState', `SPFBestGuessState', `SPFTrustedForwarderState', `SPFExplainState', `SPFBestGuess', `SPFTrustedForwarder', `SPFExplain')dnl

PLEASE SEE THE README IN THIS DIRECTORY FOR AN EXPLANATION
OF THE OPTIONS

After that you can create a new sendmail.cf with M4, like you normaly do.

Want to write something prettier and more concise, and covering
a static build?  Please do so and submit it to jcouzens@obscurity.org



*******************************************************
*********** CUSTOM CF MOD BELOW THIS LINE *************
*******************************************************

If you prefere to create your cf without M4 please make the following
changes to your sendmail.cf

Search for:   #   Format of headers   #

and make it look like: 

-- BEGIN PASTE
#   Format of headers   #
#########################

H?P?Return-Path: <$g>
HReceived-SPF: ${spfheader}      <--- ADD THIS LINE HERE
HReceived: $?sfrom $s $.$?_($?s$|from $.$_)
-- END PASTE

and then:

Search for:   H?M?Message-Id: <$t.$i@$j>

And make it look like:

-- BEGIN PASTE
H?M?Resent-Message-Id: <$t.$i@$j>
H?M?Message-Id: <$t.$i@$j>

#############################################################################################
### SPF (ANTI-FORGERY OPTIONS) ############################################################## 
#############################################################################################
#
# int (0 - 7) - Action to take based on SPF result greater than this number
# bool (true/false) - Apply 'Received-SPF:' headers to message headers?
# int (0/1) - Use 'best guess' when trusted forwarder fails? (false = off, true = on)
# text - Place SPF query language here to be executed during best guess attempt
# int (0/1) - Use trusted forwarder when SPF query returns 'none' (0 = off, 1 = on) 
# text - Place SPF query language here to be executed during trusted forwarder attempt 
# bool (true/false) - Provide explanations for any SPF result thats NOT a 'pass'?
# text - Text to expand (can use SPF macros) to provide users when SPF result is NOT a 'pass'
#
##############################################################################################
##############################################################################################

O SPFAction=1
O SPFHeaderState=True
O SPFBestGuessState=0
O SPFBestGuess=v=spf1 a/24 mx/24 ptr 
O SPFTrustedForwarderState=0
O SPFTrustedForwarder=v=spf1 include:spf.trusted-forwarder.org 
O SPFExplainState=True
O SPFExplain=See http://spf.pobox.com/why.html?sender=%{S}&ip=%{I}&receiver=%{xR} 
-- END PASTE