1) Apply the patch.

2) Add the following to your Local/Makefile:
	SUPPORT_SRS=yes
	SUPPORT_SPF=yes
	EXTRALIBS_EXIM=-L<dir-containing-libsrs2> -L<dir-containing-libspf2> -lspf2 -lsrs2

3) Build.

4) Add the following global configuration variables to exim.conf.
All variables are optional, except where stated:
	spf_debug_level          (int)
		The verbosity of the debug messages output by libspf2.
	spf_default_explaination (string)
		A quick explaination as to why a message may have been rejected.
	spf_dns_cache_bits       (int)
		The number of bits used by libspf2s caching DNS client.
	spf_local_record         (string)
		An SPF record which is inserted into ALL spf records processed,
		this allows you to accept mail from a backup MX.
	spf_use_default_whitelist (bool)
		Enables a simple whitelist built into libspf2
	srs_alwaysrewrite        (bool)
		If true, perform SRS rewriting for ALL forwarding,
		even when not required.
	srs_domain               (string)
		A domain to use in rewritten addresses. This must point only
		to machines which know the encoding secret used by this
		system. It defaults to [something sensible].
	srs_hashlength           (int)
		The hash length to generate in a rewritten address.
	srs_hashmin              (int)
		The hash length to require when checking an address.
	srs_maxage               (int)
		The maximum permitted age of a rewritten address.
	hide srs_secrets         (string)
		[required] A list of secrets with which to generate
		and check addresses.
	srs_separator            (string)
		The separator to appear immediately after SRS[01] in
		rewritten addresses.
See http://www.libsrs2.org/ and http://www.libspf2.org/ for more
information about the meaningof these variables. They are standard across
MTAs.

5) Add the following parameters to routers in exim.conf:
	forwarding_router:
		driver = redirect
		srs = forward
		data = ... [or file =, as usual]

	srs_router:
		driver = redirect
		srs = reverse
		data = ${srs_recipient}
		condition = ... [if desired]

6) Add the following parameters to your acls in exim.conf:

	acl_check_mail:

		drop    spf=fail

7) Add the following parameter into the main section in exim.conf
    
	acl_smtp_mail = acl_check_mail


8) Sit back, relax, and enjoy