OpenDKIM is an open source implementation of the DKIM
(Domain Keys Identified Mail) sender authentication system proposed by
the E-mail Signing Technology Group (ESTG), now standardized by the IETF
(RFC6376). It also includes implementations of the RFC5617) Vouch By
Reference (VBR, RFC5518) proposed standard and the experimental
Authorized Third Party Signatures protocol (ATPS, RFC6541).

The OpenDKIM package consists of a library that implements the DKIM
service and a milter-based filter application that can plug in to any
milter-aware MTA to provide that service to sufficiently recent
sendmail MTAs and other MTAs that support the milter protocol.

A user and group are needed in order to run opendkim:

groupadd -g 305 opendkim
useradd -r -u 305 -g opendkim -d /var/run/opendkim/ -s /sbin/nologin \
 -c  "OpenDKIM Milter" opendkim

You may specify alternate values if desired:

DKUSER=nobody DKGROUP=nobody ./opendkim.SlackBuild

A sample config file has been placed in /etc/opendkim.conf

The rc.opendkim script will automatically create keys for your machine's
domain name in /etc/opendkim/keys. Set AUTOCREATE_DKIM_KEYS=no there to 
disable this behavior.

Optional MySQL and Unbound support is provided. Note that MySQL
support requires OpenDBX installed. To enable:

USE_MYSQL=yes ./opendkim.SlackBuild
USE_UNBOUND=yes ./opendkim.SlackBuild

Unbound will require the unbound package which is available in SlackBuilds.