You are missing the AUTO_CONTENT line, the type should be multipart/mixed, and Dispostion should be 'attachment'. I also use a second attach.

This is the code I use in production and it works wonders.

$MIME::Lite::AUTO_CONTENT_TYPE = 1;

            #-- create the multipart container
my $msg = MIME::Lite->new (
   From     => $query->param('fromwho'),
   To       => $_,
   Subject  => $query->param('subject'),
   Type     =>'multipart/mixed'
    ) or die "Error creating multipart container: $!\n";

    #-- add the text message part
$msg->attach (
   Type => 'TEXT',
   Data => $query->param('message'),
   ) or die "Error adding the text message part: $!\n";

    #-- add the ZIP file
$msg->attach (
   Type        => 'AUTO',
   Path        => "../".$file,
   Filename    => $file,
   Disposition => 'attachment'
   ) or die "Error adding $file: $!\n";            
$msg->send;
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