use MIME::Base64;
use MIME::QuotedPrint;
...
my $body;
if ($mail->header('Content-transfer-encoding') =~ /quoted-print/i) {
 $body = decode_qp($mail->body);
} elsif ($mail->header('Content-transfer-encoding') =~ /base64/i) {
 $body = decode_base64($mail->body);
} else {
 $body = $mail->body;
}