Gee, Nigel, 1-star review much? A reading of the description would tell you about the Postfix requirement, and there are many modules on the CPAN that are less universally useful than their name would suggest. This module has other issues, like unspecified, required dependencies (f.e., Geo::IP), which might be worth mentioning instead bearing in mind, though, that it is still an alpha release. As to the author's rationale, that 'there is no single (open source) application that combines both ' ... policy and content filtering .. 'that i know of.', I believe qpsmtpd (used by, at least, perl.org and apache.org) fits that bill (though it is not on the CPAN).
No rating since I won't be using or installing this module.