my $SUBJECT="hello\n";
print "Subject: $SUBJECT";
print "MIME-Version-1.0";
print "Content-type: text/html", "\n\n"; ### THIS IS WRONG
print "Content-Disposition: inline";
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As soon as you enter a blank line everything else is viewed as content. Only enter an empty line once at the end of headers. Or, if you are unsure of the MIME standard (or indeed in a hurry), let a module take care of all that for you, http://search.cpan.org/~bbc/Email-MIME-CreateHTML-1.026/lib/Email/MIME/CreateHTML.pm looks like it might do the business for you.

By the way, did you notice that providing your code facilitated a useful answer, if you need help always show what you have tried.</snark>