I believe you cannot use URLs, so templates must be on the same server (can be on different domains, providing they are hosted on same box) - by prefixing Unix template path to template filename. For example:

my $template = HTML::Template->new(filename => '/usr/home/html/Thanks.htm');

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Cheers,

Dan
Founder and CEO

LionsGate Creative
GoodPassRobot
Magelln