If you were using the Mail::Mailer or Mail::Send then you could use their options to set the mail headers. CPAN also has a Mail::Bulkmail module which would seem to be tailored to make your job a lot easier.

--
<http://www.dave.org.uk>

European Perl Conference - Sept 22/24 2000, ICA, London
<http://www.yapc.org/Europe/>