my $message = "MIME-Version: 1.0\r\n";
$message .= "Content-type: multipart/alternative;";
...

$message .= "To: " . $self->{ToAddress} . "\n";
$message .= "From: " . $self->{FromAddress} . "\n";

if($self->{TextMessage}) {
...
     $message .= "Content-type: text/plain;\n";
     $message .= "charset=\"iso-8859-1\"\n";
     $message .= "Transfer-Encoding: 8bit\n\n";
     $message .= $self->{TextMessage}."\n";
}

if($self->{HTMLMessage}) {
...
     $message .= "Content-type: text/html;";
     $message .= "charset=\"iso-8859-1\"\n\n";
     $message .= $self->{HTMLMessage};
}
...
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