spf -- expand and report on a given domain's SPF policy

The syntax for the Sender Policy Framework (SPF) definition via a DNS TXT record is complex and expansion and inspection of the final ruleset requires possibly multiple DNS lookups.

The spf utility can be used to easily expand a domain's policy and report on its definition from the command-line.

For a longer discussion of SPF, please see this blog post: https://www.netmeister.org/blog/spf.html

Requirements

spf(1) is written in Perl, and you will need the following modules installed:

• JSON
• Net::DNS
• Net::Netmask

On Debian and related systems, you may be able to install these dependencies with:

sudo apt install libjson-perl libnet-dns-perl libnet-netmask-perl

On FreeBSD, you can install these dependencies with:

sudo pkg install p5-JSON p5-Net-DNS p5-Net-Netmask

Installation

To install the command and manual page somewhere convenient, run make install; the Makefile defaults to '/usr/local' but you can change the PREFIX:

$ make PREFIX=~ install

Documentation

Please see the manual page for all details:

NAME
     spf - report on the given domain's use of SPF

SYNOPSIS
     spf [-Vhjv] [-r address] domain

DESCRIPTION
     The spf tool allows you to inspect the Sender Policy Framework DNS records
     for the given domain.

OPTIONS
     The following options are supported by spf:

     -V		 Print version information and exit.

     -h		 Display help and exit.

     -j		 Generate output in json format.

     -r address	 Explicitly query this resolver.

     -v		 Be verbose.  Can be specified multiple times.

DETAILS
     The Sender Policy Framework (SPF) defined in RFC7208 specifies the format
     for the SPF DNS entries a domain may choose to apply.  These entries can
     range from the straight forward to the complex, harboring certain surprises
     or unintenionally obscuring important information, such as when one domain
     includes the SPF records of another domain.

     spf can be used to report on the comprehensive ruleset derived from the DNS
     record.  It does that by counting CIDRs, resolving e.g., MX records, and
     recursively looking up SPF records of any included domains.

EXAMPLES
     The following examples illustrate common usage of this tool.

     To report on the SPF records for the domain netmeister.org:

	   spf netmeister.org

     To query Quad9's public resolver for the same SPF records and report the
     results in json format:

	   spf -r 2620:fe::fe -j netmeister.org

EXIT STATUS
     The spf utility exits 0 on success, and >0 if an error occurs.

SEE ALSO
     dig(1)

HISTORY
     spf was originally written by Jan Schaumann <jschauma@netmeister.org> in
     July 2022.

BUGS
     Please file bugs and feature requests by emailing the author.