I'm not so sure that the messages can't be received by the text based clients, I just think that they don't know what to do with them. You don't need to send a multipart mail anyway if all you are sending is plain text, but I don't think that multipart/plain is actually a legitimate content type, and if it is I don't think it us going to be understood by the majority of clients. You either need to use multipart/alternative and include an HTML part or just use a single part like:

    my $msg = MIME::Lite->new(
        From    => $my_add,       
        To      => $target_add,   
        Subject => $subject,      
        Type    => 'TEXT',
        Data    => $mssg
    );
[download]

/J\