Using CentOS5/RHEL5 I needed to add some perl modules for SpamAssassin.
Note sure how important this first step is but I:
# cd /root/.cpan/sources
# wget ftp://ftp.perl.org/pub/CPAN/MIRRORED.BY
# perl -MCPAN -e shell
when asked about configuration I said 'no' and allowed the autoconfiguration to take place. I then arrived at the CPAN prompt:
cpan> install Mail::SPF::Query
cpan> install IP::Country::Fast
Perl downloaded files and asked if I wanted to install dependencies which I did. I then carried on with my spamassasin and sa-update installation.