[exim] Perl Environment

I am using a perl script with a MySQL backend to do the greylisting on 3
exim servers under cPanel.

The one server is running flawlessly but the 2 others keep soft-failing
the messages with the following in my mainlog:

-------------------------------------------------------
failed to expand ACL string "${perl{greylist}}": install_driver(mysql)
failed: Can't locate DBD/mysql.pm in @INC (@INC contains:
/usr/local/cpanel /etc/exim/perl
/usr/lib/perl5/site_perl/5.8.8/i386-linux-thread-multi
/usr/lib/perl5/site_perl/5.8.7/i386-linux-thread-multi
/usr/lib/perl5/site_perl/5.8.6/i386-linux-thread-multi
/usr/lib/perl5/site_perl/5.8.5/i386-linux-thread-multi
/usr/lib/perl5/site_perl/5.8.8 /usr/lib/perl5/site_perl/5.8.7
/usr/lib/perl5/site_perl/5.8.6 /usr/lib/perl5/site_perl/5.8.5
/usr/lib/perl5/site_perl
/usr/lib/perl5/vendor_perl/5.8.8/i386-linux-thread-multi
/usr/lib/perl5/vendor_perl/5.8.7/i386-linux-thread-multi
/usr/lib/perl5/vendor_perl/5.8.6/i386-linux-thread-multi
/usr/lib/perl5/vendor_perl/5.8.5/i386-linux-thread-multi
/usr/lib/perl5/vendor_perl/5.8.8 /usr/lib/perl5/vendor_perl/5.8.7
/usr/lib/perl5/vendor_perl/5.8.6 /usr/lib/perl5/vendor_perl/5.8.5
/usr/lib/perl5/vendor_perl /usr/lib/perl5/5.8.8/i386-linux-thread-multi
/usr/lib/perl5/5.8.8 .) at (eval 5) line 3.
-------------------------------------------------------

What doesn't make sense to me is that the include paths are all
different to what I see in the system perl environment.

Where does exim determine its perl environment from? I don't see
anything in exim.conf or exim.pl referring to those locations.


regards
Graham