use Encode qw/from_to/;
...
...

from_to($string, "cp850", "utf-8");

#!/usr/bin/perl

use strict;
use warnings;

use MIME::Lite;
use Encode qw(from_to);

my $subject = "TÄST";
my $from = "ÄÖÜ <a\@example.org>";
my $to = "lölölöß <b\@example.org>";
from_to($subject, "windows-1252", "utf-8"); 
from_to($to,  "windows-1252", "utf-8");
from_to($from, "windows-1252", "utf-8");

my $msg = MIME::Lite->new        (                
Subject => $subject,            
From    => $from,         
To      => $to,                  
Type    => 'multipart/mixed',                
Charset => 'utf-8'  );

open my $fh,"> m.msg"; # nur zum test!
$msg->print_header($fh);    
close $fh;