Build Exim with SPF support

Task: Enable Exim to use the spf acl-rule. Environment: Debian 8, Exim 4.84.2

Download sources:

apt-get build-dep exim4
apt-get install libspf2-dev
apt-get source exim4

In the sources, find and uncomment lines in ./src/EDITME:

EXPERIMENTAL_SPF=yes
CFLAGS  += -I/usr/local/include
LDFLAGS += -lspf2

Compile:

dpkg-buildpackage -us -uc -b
# ....
spf.h:15:22: fatal error: spf2/spf.h: No such file or directory
  include 
                      ^
compilation terminated.
# got an error, fix it:
apt-get install libspf2-dev
# recompile, success

Install the built package:

dpkg -i exim4-daemon-heavy_4.84.2-2+deb8u1_amd64.deb

Verify:

exim -bV

Exim version 4.84_2 #1 built 04-Oct-2016 19:48:11
Copyright (c) University of Cambridge, 1995 - 2014
(c) The Exim Maintainers and contributors in ACKNOWLEDGMENTS file, 2007 - 2014
Berkeley DB: Berkeley DB 5.3.28: (September  9, 2013)
# ... desired result
Support for:  Experimental_SPF

Prevent package updates

$ apt-mark hold exim4
exim4 set on hold.
$ apt-mark hold exim4-daemon-heavy
exim4-daemon-heavy set on hold.

# Check status
$ dpkg --get-selections | grep exim4
exim4                                           hold
exim4-base                                      install
exim4-config                                    install
exim4-daemon-heavy                              hold
exim4-daemon-light                              deinstall