I found a very simple fix - you just need to add the following statement into the header section of your Email::Simple->create 
# if email body is HTML - set content type, otherwise make TEXT
my $email_type = ($email_body eq 'HTML' ? 'text/html' : 'TEXT');


my $email = Email::Simple->create(
    header => [
    From     => $opt_param->{email_from},
    To       => $opt_param->{email_to},
    Subject  => $subject,
    'Content-Type'   => $email_type,
    ],
    body   => $message,
);

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In reply to Re: Send Email to GMAIL with html body by Anonymous Monk
in thread Send Email to GMAIL with html body by Maktub

Title:
Use:  <p> text here (a paragraph) </p>
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